Should You Climb For Rate or Gradient?

I think we all know there are two fundamental measures of climb–rate and angle. Actually I don’t like the term angle of climb, but that’s the normal terminology used for piston airplanes.

Rate of climb is the amount of altitude gained in a specific amount of time, usually expressed in feet per minute. For trip planning rate of climb is the most useful and using the appropriate airspeed to achieve optimum rate of climb for your weight is usually most efficient.

We are told to use the best angle of climb airspeed–Vx–when we want to climb as steeply as possible. A steep climb is one that achieves the highest altitude over the shortest distance.

Steep or angle are pretty useless terms when planning a takeoff or go-around. What you really need to know is how much altitude you will gain in a certain distance. That’s because the terrain or obstruction you are trying to clear is a fixed distance away and you need to know if you can clear the obstacle.

That measure, altitude gained over distance, is called climb gradient. It’s the takeoff performance requirement transport pilots must consult and be certain the airplane can achieve given weight and all other performance factors prior to any takeoff.

Climb gradient–also called simply grade by railroaders or highway designers–is normally expressed as a percentage. A 1% climb gradient in aviation terms is an altitude increase of 1% percent during a nautical mile flown, or about 60 feet.

So you know that hill is two miles away and 120 feet higher than the runway so a 1% positive climb gradient will just barely clear the ridge. You could do the math to work backward from a known rate of climb to find the gradient. Or you could apply math to find the altitude gained versus distance if you know the climb angle. But applying available climb gradient to the charted obstructions around an airport is so easy.

Some piston airplane POH climb charts include gradient along with rate, which is useful. But in the POH that do that, at least the ones I am familiar with, the data is presented only for climbing at Vy, best rate airspeed. For planning purposes you can assume that if the available climb gradient data clears obstructions when holding Vy you would have more clearance margin by flying Vx. But you wouldn’t know how much.

So the best we can do with the available data is climb initially at Vx until above obstructions and then accelerate to Vy to continue the en route climb.

Another reason to climb at the highest gradient initially is to gain the most altitude while remaining as close as possible to the runway. Wouldn’t it be wonderful if we could climb straight up to a safe altitude right over the airport. Then if an engine quit or even sputtered a return to the runway would be a piece of cake.

But we can’t climb straight up, and in most cases even helicopters can’t, but making our initial climb at Vx comes as close as possible.

Once clear of obstructions and at a safe altitude accelerating to Vy expands our options because it puts the most air under us in the shortest possible time.

If there are obstacles not far from your takeoff runway it’s worth the time to consider the maximum climb gradient your airplane can achieve. Even if the POH doesn’t have gradient data you can calculate it by factoring in the Vx airspeed and rate of climb data. Remember to correct the airspeed to groundspeed because that’s what matters so wind, temperature and elevation are all variables to consider.

After you calculate available climb gradient be sure to build in a fudge factor. In transport airplanes the fudge factor is at least 0.8%. The climb gradient measured in flight test–almost always with the most critical engine failed–is reduced by the 0.8% to determine net gradient. It is only the engine-out net gradient that transport pilots are allowed to use when planning obstacle clearance for takeoff. So it seems logical to me we should fudge at least 1% when calculating climb gradient in a piston airplane takeoff.

The lighter the airplane the closer Vx and Vy indicated airspeeds are likely to be. But even in my airplane which weighs 5,400 pounds maximum for takeoff Vy is 18 knots faster than Vx, a pretty wide margin. Whatever the airspeed difference it’s worth it to know when you need maximum climb gradient and how to achieve it and what percent it is likely to be.

Posted in Mac Clellan's Left Seat Blog | 13 Comments

The NTSB Wants Us to Stop Diving and Driving

It’s the NTSB’s job to identify aviation risks and let us know about them. It’s the FAA’s job to make rules to help contain risk. And it’s our job as pilots to understand risks and decide which we are willing to take.

For many years the NTSB has had “diving and driving” on its list of worries. But until recently there was no other way to get into hundreds, even thousands of airports, except to dive and drive. But now that has changed. And it is time to reconsider if the dive and drive risk is still worth taking.

A dive and drive is an instrument approach procedure that calls for pilots to descend and then level off and continue toward the runway. Many approaches have several steps down the procedure requiring us to dive to a new altitude, level there, and then drive to the next fix and dive again.

The big risks in a dive and drive procedure are obvious. First, a pilot may fail to level off at the proper altitude from the “dive” and fly into the terrain. The other big risk–actually the biggest, I think–is that the pilot will fail to manage the energy properly after he levels from the dive and captures the new altitude.

A pilot who blows through the assigned altitude in the dive and hits the ground has a controlled flight into terrain crash (CFIT.) Years ago before terrain warning systems, better controller radar coverage, and precise along track navigation CFIT accidents were too common. Now they are quite rare. Some pilots still fly into the ground on approaches, but in those accidents the airplane is usually out of control and thus not a CFIT.

My belief is that we now know where we are and what altitude we should be at with much greater precision and reliability. And onboard terrain warning systems and the low altitude alerts controllers radar deliver backup our improved situational awareness. We know where we are and what is a safe altitude.

But managing energy during a dive and drive has not gotten an easier. Of course, any competent pilot should be able to reduce the power to descend (dive) and then readjust the power to maintain target airspeed when “driving” level. But the workload can be high, especially for the single pilot in bumpy clouds and low visibility.

On a dive and drive you need to maintain awareness of where you are along track, know the next assigned altitude, maintain target airspeed without sinking or gaining too much speed, check configuration of gear and flaps, and–oh yes–look out the windshield for the runway.

The power adjustments on a dive and drive can be large and the airplane is usually in a higher drag approach configuration. Turboprop pilots can have the highest workload and the accident record shows too many have not gotten it right. A reason is that the propeller pitch must be very flat for the turbine engine to maintain rpm when power setting is low. The flat pitch of the prop blades are more like a disk than a prop creating a huge amount of drag. The drag is handy during the dive to the new altitude, but if the pilot fails to make a significant power adjustment when capturing the new altitude airspeed will bleed off amazingly fast. Any distraction during the altitude capture and drive can create a very serious airspeed situation.

Before RNAV approaches were developed there was no option for the dive and drive approach except at the relatively few airports that had an ILS. Even on a localizer you had to dive to an MDA. And on an NDB procedure you not only had to dive and drive, you had to figure out whether to herd the head of the needle or pull the tail just to stay on course.

But with the development of WAAS aided GPS and the LPV RNAV approaches it makes possible there is no need to dive and drive at thousands of airports. Of course, as an airplane owner you must make the investment in a WAAS aided GPS navigation system to fly the LPV, but what a return on investment.

So I think the NTSB is right. It’s time to send the dive and drive the way of the four course range, or the NDB approach for that matter. Any of us who have flown IFR for more than a few years made hundreds and thousands of successful dive and drive approaches. But each time there was at least some risk we could screw it up, and some others did. Now that there is an available alternative at thousands of runways it’s time to slide on down that glidepath in a steady and stable descent to the runway.

Posted in Mac Clellan's Left Seat Blog | 13 Comments

The Weather Is More Complicated Than We Thought

When I was in private pilot ground school many years ago the weather was pretty simple. There were high and low pressure centers, warm, cold and stationary fronts, and that was about it. Just about everything that happened with the weather was blamed on formation and movement of those phenomena.

We learned that crossing a cold front would probably subject us to turbulence in unstable air, and maybe heavy rain and thunderstorms. A warm front would bring large areas of lower clouds and visibility and wide spread precip. If you flew under one of those big “H” symbols on the prog chart the weather would be good. Fly into an “L” and you would wish you were somewhere else.

Ah, the good old days. Now we have to consider waves and troughs and ridges, a LLJ (low-level jet), and an amazing number of “disturbances” that roam around the atmosphere and can make the flying weather downright dangerous. And when helicity is mentioned watch out. You could fly into a corkscrew.

What happened to the days of worrying about only one front or one low on a trip? Now it’s not uncommon to see six, eight, even 10 or more “L” symbols on a prog chart of the U.S. mainland. Often the entire range of fronts meanders across the map frequently changing from cold, to warm to stationary along the same boundary. And on a really bad day a dry line hundreds of miles long is something to fly over, or under because it’s too long to go around.

The weather hasn’t really changed, but our understanding of it has. Actually, we have been taught a lesson in humility. We really don’t understand as much about weather, its movements and its system formations as we once thought.

The reason the weather is so much more complicated now than it was 30 or 40 years ago is that we have so many more sensors reporting conditions. Back then weather observations were made by humans, usually only once an hour. And the observers locations could be hundreds of miles apart.

To learn about what is happening aloft the weather service launched balloons carrying radiosondes to measure temperature, pressure, wind and humidity in the upper atmosphere. But the balloons only went up twice a day and then it took an hour or more to receive the data and plug it into forecasts.

Now there are hundreds of automated weather observation stations spread across the country making nearly continuous reports on weather at the surface. Many individuals even maintain their own private mini weather observation stations that feed reports into networks to be used in vast and complex forecasting software programs.

Weather balloons still go up, but something like 2,000 commercial and cargo airliners carry weather reporting equipment that automatically sends down data from the real atmosphere. Measuring wind, temperature and pressure in flight is easy, but developing sensors to automatically measure and report humidity was not. But in the past few years airliners have been equipped to measure and report that critical weather fact. And because the two big cargo airlines participate automated observation and reports aloft are pretty frequent in the middle of the night when passenger airliners are parked.

This massive amount of atmospheric data collected uses up the capacity of some of the fastest computers in the world. Every observation is a new variable to plug into the forecasting model. And when a real time observation doesn’t line up with the model’s prediction then the model comes out with a different forecast when it is run through the computer again.

The forecasters–real people–post a discussion of their forecast and thinking and concerns on each region’s NWS website at, and I love to read them. Though the actual forecast is presented in pretty cut and dry text found in terminal forecasts (TAFS) or the general public forecast of 20 percent chance of rain, high of 61 and that sort of thing, the discussion usually reveals the amount of uncertainty and many variables behind that forecast.

Are weather forecasts getting better? Absolutely. Especially the forecasts more than 12 hours out. Precip forecasts are pretty good as long as you understand the concept of probabilities. And cloud height and visibility predictions are much better than decades ago for the five mile radius around an airport that a TAF covers. En route ceiling and visibility forecasts are better, too, but certainly not as detailed as the TAF for the airport.

For pilots the most important change is the huge increase in weather observation locations. Even if the forecast isn’t 100 percent accurate, or even close, we can know what the actual surface conditions are before takeoff and as we fly along because it is reported at so many more airports. And a superb network of Nexrad radars shows us where precip is located in very near real time.

The other important development for pilots who are interested in the weather–which I think is pretty much all of us–is that the more meteorologists learn, the more it becomes apparent how complicated the weather can be. It may take more than that infamous butterfly flapping its wings to upset the forecast, but not a lot more. That “piece of atmospheric energy” I just flew through wasn’t expected, but then a “piece of energy” wasn’t on the private written all of those years ago. We just blamed it on a low, or a high, or some front or the other. Simpler times.

Posted in Mac Clellan's Left Seat Blog | 10 Comments

Why Did We Used to Do That?

I was flying my airplane to Kalamazoo for its annual. About halfway there I noticed the little red button popped on the gauge indicating a vacuum pump had failed.

Darn. There was about another $800 added to the annual bill,  I thought. But then I started to think about how not that long ago a failed vacuum pump could create a life threatening emergency.

For thousands of hours I flew around IFR in and out of the clouds with a single vacuum pump to power the essential gyro instruments. And so did lots of other GA pilots. When–not if–that pump failed the only gyro reference left was a turn coordinator, or perhaps the needle and ball of a turn and bank gyro. If you were in the clouds when the pump quit that crude gyro instrument was the only thing between you and your maker.

We all practiced “partial panel” flying using only the turn and bank to stay right side up under the hood. And we convinced ourselves we could do it. We believed if the pump or gyro quit at the worst time we could find the runway without it.

But “partial panel” control is mostly fantasy. For one, it’s impossible to practice a real gyro failure because in practice it must be simulated. You know it’s coming. The element of surprise is gone.

And the other huge difference is that the hood–and the pilot in the other seat–can’t simulate the stark terror of the real thing. Every instrument pilot can remember what it’s like to punch into the clouds by yourself for the very first time and know you can’t just take off the hood. And that’s with the instruments working.

There were many accidents blamed on loss of control after a vacuum pump/gyro failure. The only reason the accident record wasn’t worse is that even if you fly IFR all of the time at low altitudes you are only going to be in the clouds less than 10 percent of the time.

So why did we do it? Why did I do it? As I flew along in the clouds with one attitude gyro powered by one pump, and neither was all that reliable, I knew the risk. I just knew I would need luck to backup my partial panel practice if that pump quit in a wet turbulent cloud.

The reason I flew with that single gyro power source, along with thousands of other GA pilots, is that there was no other choice. If you wanted to fly IFR in piston airplanes that was it. Take it or leave it.

We accept higher levels of risk to make personal flying available and affordable. And we always will. The vacuum pump was on that list of tradeoffs that made IFR flying possible and affordable.

But risk has two major components–frequency and severity. Frequency is how often the bad event happens. Severity is the seriousness of the outcome when the risk goes bad. Vacuum pumps failed too often, and without warning so the frequency risk was high. And the severity of a pump failure could be extreme with loss of control when flying in the clouds not only possible, but even likely. And once control was lost in the clouds the results were nearly always fatal.

It’s interesting to recall that about the same time we were coming to grips with the risk of flying IFR with a single vacuum pump the V-tail Bonanza controversy was raging. The controversy was caused by the fact that in loss of control accidents the tail on some V-tail Bonanzas failed in flight, while that almost never happened in straight-tail Bonanzas.

So the focus was on the structure of the V-tail, not the loss of control that caused the failure. Most of the control losses began while the pilot was flying in the clouds. And vacuum pump or gyro failure contributed to many of those events. But the hue and cry was about the tail, not the pump reliability. To me that’s an indication of how we IFR pilots refused to admit to ourselves the severity of a vacuum pump failure and looked to place “real” risk elsewhere.

Little by little the pump unreliability problem was acknowledge and attacked. I hate to say it, but in this instance product liability lawyers did focus the spotlight on the pump and some courts found its reliability to be unreasonably poor and big judgments were awarded. A solution had to be found.

I had one of the first systems that used engine manifold differential pressure to supply emergency vacuum to the gyros. I had a system that used a clutch to engage a second engine driven pump when the primary pump failed. I had a second pump powered by an electric motor. Each of those worked, sort of, but not well enough given the severity of the risk.

Electrically powered mechanical attitude gyros were available and many installed them, but they didn’t enjoy a good reliability record, and were expensive. But then the problem was solved by a technology that almost nobody saw coming–MEMS–microelectronic mechanical systems. Those are the tiny accelerometers that, when teamed with powerful fast computer chips, make the compact low-cost non-moving electronic gyro possible.

Whether you fly a homebuilt, classic, standard category or brand new airplane an attitude-heading reference system (AHRS) is available at an appropriate size and cost. These non-moving gyros are now even portable and battery powered so they are totally independent from aircraft systems. There is absolutely no reason for an IFR pilot to ever be left in the clouds without useful attitude information.

So if you think we haven’t made meaningful progress in personal aviation, think again. Now a vacuum pump failure is just another item on the maintenance bill, not a threat to life itself.

Why, you ask, do I still have vacuum pumps? They inflate the deice boots, that’s why. Still waiting on micro electronics that can do that.

Posted in Mac Clellan's Left Seat Blog | 26 Comments

ADS-B–I Hadn’t Considered That

Almost immediately after the Germanwings Airbus A320 had crashed in the Alps a very detailed plot of its flight path was available worldwide.

The flight of the Airbus was tracked from takeoff to a final position report that ended very near where the airplane hit the mountains. The plot showed altitude, groundspeed, vertical speed and track in detail. It was immediately apparent that the airplane made a fairly rapid but steady descent from cruise altitude to impact with the speed essentially constant.

It’s the first major accident I can think of where such flight path detail was immediately available to everybody and it’s all thanks to ADS-B.

Radar has, of course, tracked a number of doomed flights in the past. But radars are under the control of government agencies and it usually takes weeks, months or even years before radar plots are released. And radar is surprisingly imprecise and coverage gaps are common.

But the details of the A320 flight path were posted on websites around the world and hashed over on TV and internet sites very shortly after the accident. The onboard flight data recorder will have more information such as indicated airspeed, flight control positions, power settings and so on, but the recorder won’t have any better, or even as good, a track of the actual flight than what was available to all instantly.

What is at work here is the automatic operation of ADS-B. That’s what the “A” stands for–automatic. Once ADS-B equipment is installed it goes about its job of automatically sending out the identity, position, altitude and velocity of the airplane, including while the airplane is still on the ground. ADS-B updates that information with a new broadcast at least once per second and the accuracy is within a few meters.

Compare that to how radar and transponders work. A radar requires a directional antenna to determine the azimuth from the radar site to the target. Radar also needs to time the round trip of a transmission and reply to determine distance from the site. That yields a bearing and distance from the radar site to the target.

For its part the transponder in our airplanes does nothing until it is interrogated by a radar or traffic detection system in another airplane. When it is interrogated the transponder can only reply with our identification–the four-digit discrete code and the unique ICAO code if the transponder is Mode S–plus the pressure altitude data of Mode C.

So the radar equipment must plot the bearing and distance information to establish the actual location of the airplane. Then the electronics mix in the Mode C reply to determine altitude. After several radar “hits” an approximate flight path can be determined including ground speed, vertical speed, altitude and track.

But even short range radars get new “hits” only every couple or three seconds, while long range radars may get a new return only every seven or more seconds. That’s a long time when an airplane is moving at more than 400 knots as the Airbus was for the entire descent.

ADS-B is, however, reporting its actual position and velocity. There is no need to plot anything. ADS-B automatically says “I’m here, at this altitude, flying this fast, with this vertical speed, and along this track” all based on the global lat-long grid. All you need is a very simple and inexpensive receiver to know everything about an airplane with ADS-B. Radar needs a vast network of huge hardware and computers that only governments can afford.

The FAA has installed more than 600 ground stations to receive and process ADS-B data. But private networks are installing thousands more receivers around the world and linking them via the internet. Individuals participate by assembling a receiver and hooking it up to their computer. That means soon there will be complete ADS-B reception coverage nearly everywhere except over the open oceans.

The wide open nature of ADS-B data worries many who are concerned about privacy and security. And that’s a valid concern.

But there is an ADS-B benefit I hadn’t considered before this accident. For the first time accident investigators will have precise and detailed information about the flight path of an accident airplane that is nearly as useful as a flight data recorder. In most general aviation accident investigations there is very little to go on. Sometimes there is a radar plot but it’s usually incomplete and certainly not precise. But with ADS-B installed in most airplanes in a few years we can know much more about what happened in an accident, even though, as in the case of the A320, we can’t immediately know why it happened.

Every new technology is designed to solve a problem or create a new product or service, but there are always unexpected issues. It is the same with ADS-B. The system is designed for traffic surveillance and separation, but the immediately available flight path data will also bring unexpected and unintended other results. What will they be? Only the years ahead will tell.

Posted in Mac Clellan's Left Seat Blog | 33 Comments

You Gotta Love The T-Bone Approach

For decades when I got to pick my landing airport I always went for one with ATC radar coverage. Being vectored for the approach is safer because you have a second set of eyes watching where you are and tracking safe altitudes.

The safety edge of radar vectors became automated years ago with low altitude alert software installed in the controller’s radar. Even if the controller doesn’t notice you deviating from a safe altitude for your position the software sees it and sounds a loud alert that the controller passes on to you.

But I have to say that safety was really secondary in my thinking. The real reason I wanted to land at airports with radar coverage is speed and convenience. Radar vectors for an approach were almost always less complicated–and thus less time consuming–than flying to an initial approach fix followed by some sort of course reversal or holding pattern before you actually got started down final approach to the runway.

And if you were unlucky enough to arrive in the airport area when there was another IFR flight around you could be delayed many minutes waiting for that airplane to cancel IFR so you could start the approach.

I’m using the past tense here because the situation has changed thanks to thousands of new GPS based RNAV approaches. Particularly WAAS-aided LPV approaches that nearly all have the T-bone configuration.

Stancie and I were headed home to Michigan from the Bahamas last week. Because of the requirement to stop in Florida to clear U.S. Customs we need a fuel stop en route. In the past I had used Lexington, Kentucky because it has good approaches and radar. But the London airport also has a long runway, good approaches, and fuel that is at least a buck fifty cheaper and is only about 60 miles away. But London has only limited radar coverage from Indy Center while Lexington has full approach control at the field.

The weather was low over most of the southeast that day. It was forecast to be above minimums for London but it was almost certain that flying an approach would be necessary either there or at Lexington.

But London, like thousands of other airports, now has GPS based LPV approaches to both runway ends. And the approaches are the T-bone type which simplifies the approach to match or maybe exceed radar vectors for convenience and ease.

The T-bone configuration has two initial approach fixes astride the initial fix that is on the extended centerline forming a T-bone shape. The fixes at the end of the bone are five miles or so from the final approach centerline.

Because of the precision of WAAS GPS, and the turn anticipation logic that is built into approved navigators, you fly directly to the initial fix closest to your position. The distance countdown to the fix plus the turn anticipation command makes it easy to turn onto the new course without overshoot, something almost impossible with old VOR, NDB or localizer guidance. With those analog signals you didn’t know for sure you were nearing the course until the needle started to move, and that was usually too late to turn more than a few degrees without overshooting.

About 40 miles south of London I asked the Indy controller for clearance to UNMODE, the T-bone fix on the south end of the LPV approach to Runway 24. He issued the clearance, I selected it from the initial approach fix options offered by the Garmin GNS 530W and that was it.

The 530W guided me to UNMODE, directed me through the about 40 degree heading change to ODUBE on the final course. Nearing ODUBE the box again anticipated the turn of 90 degrees so I watched the moving map show my track turn nicely inside the fix and center up on final. Once established the 530W switched automatically to LPV approach mode and had perfect ILS-style guidance to the runway.

There is no way radar vectors from my northerly en route course around to intercept the Runway 24 final could have been shorter or easier or quicker. And I had perfect situational awareness at all times during the approach. And the 300 foot decision height and one mile visibility minimums are the same for the LPV as for the actual ILS that serves Runway 6 at London.

I am dubious that the satellite based navigation advancements and ADS-B surveillance of NextGen will add capacity at the nation’s truly busy airports because runway capacity, not so much airspace, is the limit there. But at the thousands of little used airports across the country the LPV with its T-bone shape is cutting flying time and increasing situational awareness greatly compared to old analog guidance approaches.

So if you fly IFR we are now getting payback for the investment in advanced WAAS GPS navigators. The T-bone and LPV have made the thousands of little used airports as convenient as those with radar. And the TAWS terrain warning that is available in most WAAS navigators provides the backup the software in controller’s radar does to alert us of a mistake. At least these parts of NextGen are living up to our hopes.

Posted in Mac Clellan's Left Seat Blog | 4 Comments

We Are Pilots Forever

I received the notice that I had to renew my driver’s license. The good news–if there was any–is that I could do it online and the state would simply reuse the photo from last time.

As I was entering the credit card number to pay for a few more years of driving privileges it crossed my mind that I had never renewed my pilot’s license. There is no expiration date on the certificate. I guess it expires when I do, but I can’t find that in the FARs anywhere.

Over the 45 years or so of flying I have had a whole bunch of different actual certificates. Every time I added a new certificate level or a new rating, along came a new piece of paper. Each carried a date of when it was issued, but none listed expiration.

Most recently I was issued the plastic card with nearly illegible printing. My friend and aviation writing legend Richard Collins and I joked at the time that the new tiny type was actually an eye test. If you couldn’t read that faint small print, you couldn’t fly. I’m close.

There are at least two pilot certificates that I can think of that do expire–the CFI and the student pilot. The student pilot certificate limit makes sense. After all, we want people to progress toward the private and not be students forever. I guess the term limit on CFIs also makes sense because the FAA wants to be able to update and change the emphasis of pilot training. Renewing the CFI puts the instructor in contact with the FAA or its approved courses which provides the opportunity to remind instructors of what the FAA now thinks are the most important topics to reinforce during instruction.

But the same case could be made for limiting the duration of any pilot certificate. But the FAA doesn’t. I wonder why?

The rules have a wide open backdoor requiring renewal in the form of an FAR 61.56 flight review every two years. All of us, at a minimum, must complete the review to legally fly. But the results of the review, when it happened, what topics were covered and so on are not reported to the FAA. The review is not a pass or fail check but a minimum of an hour of ground and then hour of flight review with a CFI in any airplane you are rated to fly.

The FARs pile on other requirements to keep your license valid to carry passengers or to fly IFR, or to fly in airplanes requiring type ratings. But to fly solo under VFR in a basic airplane a flight review every two years will meet the minimum requirements.

The FAA isn’t nearly so lax in wanting to know where we live. You must have on file your current permanent mailing address. If you move you have to report the new address within 30 days. And a P.O. Box or general delivery address won’t do. You must report a location. And if your residence doesn’t have an assigned address you must provide the FAA with specific directions on how to find the place.

I’m not sure why the FAA is so focused on where we live but doesn’t ask or record how much or even if we fly. Is it some morbid leftover from a need to find next of kin? Maybe.

The medical certificate does give the FAA a more or less steady flow of information on pilots, at least enough to know the pilot was still alive at the time of the medical examination. That’s how the FAA determines you are still an “active” pilot. And you remain “active” for the duration of your medical certificate’s valid period which is two years for we older types and five years for the under 40 crowd.

But even that every two or five year sample of pilot’s continued existence is about to change. Already pilots flying to the sport pilot rule don’t need a medical. Neither do those flying gliders or balloons. And soon, one way or another, the ability to fly privately using a driver’s license instead of medical will be expanded and more “active” pilots will disappear from the rolls.

So here we are in what appears to be the most highly regulated activity in the nation–flying–but the government knows very little about us. On the other hand, the states keep pretty close tabs on us as drivers demanding a new license be issued every couple or three years. Even our dog’s license expires every three years. But as pilots we fly on forever. Pretty good deal.

However, real life doesn’t work exactly that way. A friend in Florida was recently taking care of the estate of his recently deceased very elderly mother when he came across a new Florida driver’s license that was issued and put into the mail to her several days after her death.

On paper–now plastic–we can be pilots forever. In Florida, at least, I guess you can be a legal driver for longer than anyone would guess.


Posted in Mac Clellan's Left Seat Blog | 20 Comments

Airplanes Hate Cold Weather

I find it very strange that airplanes can do so well with very, very cold conditions after they are in the air, but have all kinds of trouble with unusually cold weather on the ground.

We all know about congealing oil and other problems with starting a very cold piston engine. Most piston airplane owners in the cold country have installed heaters that warm at least the oil, and some heat up the cylinders, too.

But cold soaking brings on lots of other potential problems that engine preheat just won’t address.

In my experience very cold conditions almost always attack anything that’s inflated. Tires, for example, always lose at least some pressure. That makes sense because cold air–or nitrogen or any other gas–takes up less space than when warm. The air doesn’t need to leak out of a tire for it to lose pressure.

And airplane tires are pretty small compared to a car tire so they hold a smaller volume of gas, and usually at a higher pressure. My little six-inch nose tire is supposed to be pumped up to 60 psi. Check the pressure after a really cold spell and it’s often down in the 20s without a leak, or at least a leak a patch can fix.

Another airplane system that loses pressure with cold temperature is an oleo strut. The gas pressure is retained by O ring seals. Cold shrinks the O rings by at least a little and there goes some of the gas. Since oleos function at very high pressure compared to tires, it doesn’t take much of a gas loss to drop the gear strut down to a risky level.

It’s usually the first few cold days of winter that calls for servicing the landing gear struts, and with luck that added gas volume may get you the rest of the way through. But if you have a really below average cold snap like we have had in the northern tier of states the strut can easily go flat again. The O rings aren’t necessary bad, and new O rings probably won’t change anything. It’s the darn cold.

Fuel tanks, fuel pumps, fuel hoses and especially fuel bladder tanks really object to being cold soaked. If all the connections are tight and O rings and gaskets are in good shape you may make it through those sub-zero nights. If not, you’ll find the weak point.

That’s what happened to me when I went to launch for the Bahamas after days of zero or even below, which is very unusual for us being right on the shore of Lake Michigan. It was many degrees colder inland, but that didn’t help me.

The main gear struts were clearly down, the tires needed a shot of air but that looked like my only problem. Until the fuel truck topped the tanks. Then avgas started to run out of the fairings under the wing root and drip of the trailing edge of the flap. More like a stream of fuel than a drip.

Well, I thought that was the end of our trip south and that one of the three fuel bladder tanks in the wing would have to be replaced. But the experts at Executive Air on Muskegon Airport where I base quickly found a cold related, but less serious problem than a bladder leak.

What had happened is the cold shrank the gasket that sealed an access port into one of the bladders where the fuel quantity sensor is located. The screws holding the access plate were safetied but between the screws working a little loose and the cold shrinking the gasket fuel was running out. Tightened screws and a gasket and the leak was fixed.

Something similar happened last year when the airplane went in for annual. There were some fuel stains around one of the bladder tanks. But as soon as the airplane warmed up in the shop there was no sign of a leak that could be found. Some fuel seeped from somewhere in the cold, but stopped seeping when warm.

But we fly airplanes up into cold air, very cold air at higher altitudes. Standard temp at jet cruise level is -56 degrees C. And airplanes seem to do fine with that cold. Why?

The difference is that we climb into the cold with the airplane and its systems operating instead of subjecting them to extreme cold at rest. An operating airplane warms itself in many ways, and most airplanes can’t remain aloft long enough to match the hours or days of a ground cold soak. Some very long range airplanes that stay at high and cold cruise altitude for 12 or 14 or more hours have had trouble with fuel freezing or water being trapped where it can freeze and do damage, but that’s not an issue for most of us.

That’s why for certification jets and other transport airplanes must undergo cold soak testing. The airplane has to be flown to some extremely cold location, left outside for hours, usually over night, and then wake up and function without any added heat. It’s a tough test.

My airplane like other piston airplanes didn’t have to survive a cold soak test for certification. And it may not have passed. But at least it’s warming up now here in the Bahamas hoping for warmer conditions when it gets back to the shore of Lake Michigan.

Most of us think airplanes have personalities, and mine does. It now hates the cold in its old age a lot like the pilot who flies it.

Posted in Mac Clellan's Left Seat Blog | 3 Comments

Airplane Windows Add Safety–And Comfort

Plenty of window area in this Sonex

The largest possible window area is obviously a safety advantage when it comes to seeing and avoiding other traffic, or even when looking at the runway while landing. That’s why most fighters and aerobatic airplanes have transparent canopies.

But windows also add–or detract–from comfort for all occupants of an airplane. The right window design makes any cabin feel more spacious and welcoming, and can also ease the discomfort of turbulence.

The Klapmeier brothers understood this when they were laying out the original design for the Cirrus. That’s why the SR20 and SR22 have big windshields, large windows in each door, and even more importantly large rear windows. In many airplanes passengers in the second row are left sitting down in a cave with a very limited view of the outside world. But not in a Cirrus. The brothers had flown enough with family members and friends in the backseats of other airplanes to understand how important this is.

Another design that did a nice job with the windows is the Bonanza, and the many Beech models it spawned. In the Beechcrafts the windows sweep up into the overhead helping to make the cabin feel larger than it really is, even for the second row of seats.

The epitome of window perfection is the Gulfstream line of business jets. In the late 1950s when engineers at Grumman were creating the stately Gulfstream I turboprop–the first purpose built turbine business airplane–they included huge oval windows in the cabin. Passengers loved them, and every Gulfstream since has had the trademark ovals. In fact, for the super speedy and super ultra long range G650 Gulfstream increased the size of the oval windows by nearly a third.

But big windows come at a price. It’s not that the transparent material costs so much, but the structural accommodations required to design in large windows is costly and heavy. And then there is the cost of annoyance and suffering when you just don’t want all of that sunlight beating in on you.

The structural penalty for big windows is mostly in weight. No matter what material the actual transparency is made from it can’t carry structural loads. That means the load carrying elements of the airframe have to be designed around the window opening instead of following their most efficient path.

In unpressurized airplanes the weight and materials costs of larger windows isn’t nearly as great as in pressurized airplanes. Perfect examples of the window size penalty in pressurized airplanes are the P Baron or the Cessna P210. Both pressurized airplanes evolved from unpressurized versions and in each the window size was cut down markedly to reduce the amount structural and transparency strength required, and thus help control weight.

In transport airplanes windows need to be redundant so failure of one layer or pane of the transparency won’t create a decompression so you can see how the weight of a big window adds up. And in the cockpit windshields and their frames have to withstand the impact of a large bird at 250 knots. Add in the heating elements and it’s easy to see how a big windshield, no matter how much pilots love them, adds weight plus construction and maintenance costs.

Early Citations are an oddity in windshields, birds and the FARs. The Cessna business jets had two Vmo (maximum indicated airspeed) limits, one for below 8,000 feet and a higher red line for above that altitude. The reason is that the airplane met the bird impact rules at the lower Vmo but, under the rules, the birds that endanger the windshield did not fly above 8,000 feet. I always wondered if the birds had read the FARs, or had altimeters for that matter.

The primary price pilots pay for big windows comes when the sun is shining. The greenhouse effect is no myth. Sit under a transparent canopy on a sunny day for very long and you are soon wishing for shade, even if it’s cold outside. Most pilots and builders of canopy airplanes devise a shade of some sort to pull over the center of the overhead for relief. But even with a shade it can quickly become unbearable under the canopy on a hot sunny day, especially on the ground.

Big windshields also extract a toll in suffering when flying toward the sun. The pilots who suffer most are those on the transatlantic routes. Flights typically leave the U.S. in the evening but the crew quickly catches up with the rising sun in the east and are broiled for the second half of the flight and arrival. The return trips usually depart in the late morning and chase the sun across the ocean assuring the pilots will be blinded and toasted for the entire trip.

Nearly all passenger cabin windows have screens and blinds to pull so being blinded and cooked is mostly a pilot problem. Pilots have propped up just about anything in the cockpit windows to block the blinding glare. And one company, Rosen, has made a very successful business of building articulating arms that allow you to position the sun visor almost anywhere over the cockpit windows. Designers of new airplanes are including effective sun glare protection devices in the original layout of the cockpit. It’s that important.

But no matter how annoying the sun may be, I still prefer being in an airplane with well designed windows. I can usually come up with some way to shade myself when needed, but there is nothing you can do to change that little slit of a windshield that is left in too many airplanes as the instrument panel glareshield has risen to accommodate ever more avionics displays.

And if you want to know what passengers think of the importance of windows just ask a Cirrus or Gulfstream salesman. They know.

Posted in Mac Clellan's Left Seat Blog | 8 Comments

What the Heck is WAAS?

WAAS has been in the news a lot lately as airplane owners study the coming ADS-B mandate and how to deal with it. We are constantly reminded that the crucial element of ADS-B “out” is a position sensor that uses WAAS-aided GPS.

WAAS stands for wide-area augmentation system. Or if you want to be one of the avionics cognoscenti you would call it SBAS for space-based augmentation system. Neither one of those terms says much about what WAAS is and how it works.

The bottom line information is that WAAS corrects errors in the GPS navigation solution over a wide area. The “wide area” for WAAS is pretty much all of North America, plus offshore water on both coasts and most of the Caribbean. WAAS compatible systems are in place or being constructed by other nations around most of the world.

As I’m sure you know GPS uses a constellation of satellites orbiting the earth at an altitude of about 11,000 miles. The GPS navigator detects the travel time of signals from several satellites to calculate the distance to each of those satellites. The position of the satellites is known so the GPS navigator triangulates using the measured distance from the satellites to establish a 3-D position.

Unlike a radar, or DME, that use a timed round trip of an electronic signal to calculated distance GPS relies on an extremely precise clock. When a GPS receiver locks on it synchronizes its clock to the satellites. The satellites in turn are synchronized to supremely accurate clocks on the ground. With all the clocks in synch the GPS navigator knows exactly when the signal left the satellite so it can calculate how long it took the signal to reach the receiver and thus calculate the distance from the satellite.

Basic GPS has a useful accuracy of around 10 meters though rarely errors can be larger, possibly as much as 100 meters. Errors in the GPS solution come from slight variability in the clocks, small position errors for the satellites, but most importantly, from distortion as the weak signal travels through the earth’s ionosphere and atmosphere. Ten meter accuracy–about 33 feet–is plenty good for en route navigation, and even for non-precision instrument approaches. But that isn’t nearly good enough for precision approaches. And the errors in vertical calculation are particularly troublesome when you want guidance to within a couple hundred feet of the ground without being able to see it.

WAAS corrects these fundamental GPS errors so that nominal accuracy both laterally and vertically is better than 2 meters.

To work its magic WAAS employs a network of ground stations at precisely surveyed locations. These stations know exactly where they are so they compare that known position to the real time calculated position from “raw” GPS signals. The WAAS ground stations create an error correction signal that is sent up to non-GPS communication satellites that are in geostationary orbit. The WAAS correction signal then comes down to a GPS receiver along with the basic GPS signals and the errors are corrected in the airborne navigator.

Equally important to the position error correction is what navigation types call “system integrity.” Basic GPS provides a position fix at one hertz, or once per second. That sounds fast, but consider that if you are flying an instrument approach at 120 knots you will cover 200 feet each second. If a position fix is missed because of some kind of signal problem you will travel another 200 feet before the next possible fix. By the time the navigator is sure there is a problem you will have gone many hundreds of feet, way too many when flying in the clouds close to the ground.

WAAS enables a navigator to fix its position six or more times a second so there are multiple opportunities to find an error. WAAS also contains information on the integrity of the system and sends a quick warning of a problem. So with WAAS a pilot will see a warning flag very quickly if there is a navigation problem, which is exactly what you need when flying a precision instrument approach.

The creators of the ADS-B NextGen system found these WAAS capabilities to be essential if the system is going to allow reduced separation of IFR traffic. If we’re going to fly closer together while in the clouds we obviously need–both controllers and pilots–to know exactly where we all are in 3-D. We also need to get the earliest possible warning if the system is failing or unacceptable errors are creeping in. That’s why WAAS, or a navigation system that equals WAAS-aided GPS, is required as the position sensor for the ADS-B out signal.

I’m unwilling to wager that even with the surveillance and navigation precision of WAAS and ADS-B that we will reduce IFR traffic separation in a meaningful way. The technology makes it possible, but I’m not sure that emotionally pilots or the public want to fly closer than 3 miles from another airplane at the same altitude in the clouds. And even if you do fly closer, will there be enough room on the runway for the airplane ahead to land, brake and turnoff?

The precision of WAAS and ADS-B makes virtually no sense for the VFR pilot where even the worst 100 meter navigation accuracy is more than enough, and missing other traffic by at least a mile, not a few meters, is the goal. But so far the FAA is sticking with its single standard of WAAS for ADS-B position sensing for big jets and little pistons.

Posted in Mac Clellan's Left Seat Blog | 17 Comments