Airframes Need Experience, Too

Sikorsky helicopter president Jeff Pino was talking about the company’s S76 twin engine helicopter that will soon be offered in yet another evolutionary version, the “D” model. The S76 has been in production since 1979 and continues to be one of the most popular helicopters for executive use, along with serving the offshore oil industry, emergency medical service and many other vertical lift missions.

What Pino said is “there is no regulatory replacement for actual experience” referring to the outstanding safety record of the S-76. It suddenly dawned on me that every pilot or aircraft manufacturer knew this years ago, but some have lost sight of this proven fact in recent years.

What makes Pino’s observation even more remarkable is that he presides over a company spending a fortune on developing new technology. Sikorsky won the Collier Trophy last year for its X-2 coaxial rotor helicopter that set new speed records for a helicopter. Pino clearly knows we must constantly search for ways to improve, but he also knows the value of technology proven over decades in service. New rules are necessary, but only experience can work out the unknowable issues.

The objective of every change made to certification rules for any kind of aircraft is improving safety. Regulators are aware of accident causes as we all are, and they attempt to eliminate the causes of past accidents with new rules. In theory, adjusting the certification standards to enhance safety makes sense, and sometimes it works.

An example of a certification change that added safety is in fuel management. Airplanes certified in the 1950s and 60s could have multiple fuel tanks, including main tanks and aux tanks and restrictions on when to use each, and strict requirements for pilots to monitor fuel status and select the proper tank.

In tip tank Cessna twins, for example, the tips are the mains and aux tanks are in the wings. When you switch from main to aux the fuel “vapor” return from the fuel injection system goes back to the main tank even though you have selected the aux tank. So when flying on the aux tank the main tank will actually be gaining fuel because of the vapor return. Does that make sense to anybody?

Some airplanes were approved with a single fuel gauge for more than one tank. But that gauge didn’t necessarily change its reading to match the selected fuel tank. You could be drawing fuel from one tank while the fuel gauge was showing the level of another tank. Is that a potential pilot trap? I think so.

Current certification rules don’t allow the complex fuel management systems that we once took for granted and one more opportunity for a pilot to make a mistake has been removed. That’s a good thing.

But other certification changes added complexity to perhaps avoid something that may happen, even though it hasn’t. For example, some piston airplanes now must have a means to break out a window to escape after a crash in case the airplane is inverted or the door jams. Could that happen? Of course. Has it been an issue? Not that I know of.

The reality is nobody can predict what problems will really arise in any airplane or helicopter until it is out in service. All sorts of methods have been devised to perform accelerated testing that simulates actual use but the tests have been only a little helpful. Regulators try to predict how pilots or maintenance people will perform in the real world, but with limited success. So far nothing replaces time and experience, except time and experience.

So when an aircraft like the S-76 has been flying in all sorts of conditions, all over the world, and with an enormous variety of pilots and maintenance people involved for more than 30 years, we learn where the real safety issues are. And they get fixed.

I am not anti-progress, and I love to see newly designed aircraft come along, but I know that an evolutionary design is hard to beat.

At one time nobody wanted serial number one, or 10 or maybe even 50. Some manufacturers of all sorts of products have even faked it a little by starting production with a higher serial number. I understand.

Jeff Pino is a helicopter pilot, of course, but also owns and flies warbirds so he has an appreciation for the importance of historical aircraft and the experience of owning and operating them. And he also knows that helicopters, even more than airplanes, benefit from years, even decades, of refinement of a solid basic original design. After all, I believe the original design of the Sikorsky S-61 helicopters that carry the president may be older than this president. Experience does matter.

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2 Responses to Airframes Need Experience, Too

  1. Dov Elyada says:

    Mac must be living and flying in a country where all regulator people are saintly, with only our safety on their minds, well balanced by our civic liberties and financial interests. I envy him. At least in the flying environment I know, at least some of them are there to enjoy practicing bureaucratic power over us while covering their behinds to the best of their abilities.

  2. roger russton says:

    The flipside is that designers need experience too. We’ve lost a lot of design experience by keeping a lot of designs in production, or maintained as front line military aircraft, far longer than makes any objective sense.

    Designing and building a new airplane is something you really learn only by doing. When we make an evolutionary change to an old design we wind up enshrining things that once made sense but no longer do, and inevitably some making no sense then or now.

    There are aspects of the B-52 structure that are a kluge because the prototype XB-52 had a B-47-like cockpit layout. A B-36 has never flown in my lifetime and I am pretty close to fifty. The B-47 was retired when I was in diapers and the pre-H model B-52s have been scrap for a decade and a half. Yet we are planning to keep the H flying until 2050 or until one going into a packed WalMart due to structural fatigue makes it politically infeasible. If a subsonic aluminum aircraft was going to do the job we should have built a similar replacement decades ago. I can’t believe a variant of some Boeing airliner airframe could not do that job at drastically reduced cost.

    Another example is the JPATS, which was pure pork (and I say that having lived in Wichita). They started out with a Pilatus PC-9 and more than doubled the price,making it more expensive than had they designed an aircraft from scratch. Ab initio training in a five million dollar airplane is so insane I can’t describe it.

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