Your Roof is Gonna Leak . . .


I am a pilot. I am lucky to have retired without incident from a career at an airline. Flying is still in my bones.

Mine is an apprenticeship trade. You can’t learn it in a classroom or by reading a book, although both help. You have to get your hands on an airplane.

Most trades are like mine. It takes constant study to stay current in the field. The reference books, software, and reams of data relevant to the job are huge and growing. But the essential learning, the learning that serves as backbone and basis for all the stuff in the reference books, is hands-on experience taught by a mentor and teacher. In turn you should pass this knowledge on to the next generation.

Tradespeople are no better and no worse than others. The majority of them like going to work and doing the the best job they can. There is satisfaction in building something or in accomplishing a mission. You can look back and say, I built that, or I did that.

But like rule of law or paying taxes, plying a trade with skill and devotion is a social contract. Protect me from lawbreakers, ensure others pay their fair share. Give me a living wage so I can support a family, and respect my work for what it is.

Nor are we tradespeople to be divided from business people, put in a separate category. On the contrary most small businesses are founded and powered by tradespeople, be they plumbers, machinists or software engineers with ideas. Entrepreneurship and the trades are interdependent and have been since the days of the guilds. Perhaps what we are less compatible with is management.


I was lucky also to have spent most of a decade flying and teaching on Airbus aircraft. The design of the A320 is revolutionary, extraordinary, and even beautiful. She never failed to delight me (like mariners, I thought of my ship as a person, a female) and she remains one of the loves of my life.

But she is not perfect. Call it my fallacy of anthropomorphism if you will, but I believe that a man-made object cannot be more perfect that the sum of its creators. It can be outstanding, it can be beautiful, but it cannot be perfect. Lovely as she is, my Airbus is no exception. She has her faults.

Her qualities have been called to review by two recent events with very different outcomes: Chesley Sullenberger's heroic handling of a ditching in the Hudson River, and the crash of an A330 in the Atlantic Ocean with the loss of all on board.

All airplanes have what is called an envelope. Fly faster than Va (maneuvering speed) and turbulence or rough handling can result in damage to the airframe. Fly slower than Vs (stall) and the wing can no longer generate enough lift to hold the airplane up. Fly faster than Vd (dive speed) and all manner of bad things can happen, from Mach tuck to control flutter to loss of control. The technicalities of the flight envelope can fill a book and have, many times over. The parameters include aircraft weight, air density (altitude, temperature) and G loading. But the bottom line is that it is the pilot's responsibility to keep the airplane in the envelope, to fly it as it was designed to be flown.

Bernard Ziegler had a different idea.

He was my love's Daddy. You see him in her everywhere you look. She is beautiful, intelligent, accomplished, and refined. She is uncompromising. She is very French.

She has an envelope like any other airplane. She flies with the same aerodynamics as they do. But her Daddy added a new feature to her design: envelope protection.

With the A320 and subsequent models, the pilot cannot “push the envelope”. He can push or pull as much as he wants and she will go to the edge, but not over the cliff. She is impossible to stall.

As long as she is in NORMAL LAW.

Her fly-by-wire control system is impressive in the extreme. There have been no known failures in service. But like us she depends on sensors, eyes and ears. And of course electricity to power her hundreds of computers. Starve her, blind her, or deafen her and you are asking for trouble. Chesley Sullenberger understood her. His first act was to reach up and start the Auxiliary Power Unit. This one strategic move kept power on the aircraft busses as Jeffrey Skiles, the First Officer, went through the engine restart drills. This one strategic move kept her in Normal Law until touchdown.

AF447 was approaching the Intertropical Convergence Zone, the ITCZ, the doldrums. It was night and as usual there was a long line of thunderstorms in the Zone, crossing their track obliquely. The Captain had just left the Flight Deck for his planned rest. The most junior pilot – the relief pilot – was in the left seat flying the aircraft.

Ahead of them a small storm was showing on the radar. Despite its size it was dense enough to reflect all of the energy from their radar. The result – a well-documented phenomenon called attenuation or blanking – was that a gap appeared in the line behind the small storm. AF447 flew around the corner and suddenly the gap was gone. They were plowing into the main line of thunderstorms.

Supercooled water is unusual at FL350 but not unusual in thunderstorms. Drops of supercooled water freeze instantly when disturbed – as for example by a fast-moving aircraft. The temperature that night was an unusually warm minus 40 C., just warm enough to keep the drops from freezing and cold enough so the heating elements in the A330's pitot probes were not powerful enough to keep the probes open. All three pitots were temporarily blocked, cutting off all airspeed information.

She was blind and deaf. Panicked, she shut down her envelope protection and called out to her pilots for help, shutting down the autopilot and autothrust and reverting to Pitch Alternate Roll Direct Law. Visual and aural warnings cascaded across the ECAM and into the speakers. Beautifully designed and prioritized for foreseeable failures, the warnings that night became a powerful distraction, demanding the pilots' attention at just the moment they needed to ignore her.

She was squealing like a stuck pig. If the pilots could have read her right that night, what they would have heard was, I'm gone, guys. I'm outta here. You have control.

Blind, deaf, and still squealing, the A330 handed control to the relief pilot. He pulled back on the sidestick. She zoomed upwards, climbing to FL380 at 7000 feet per minute, rapidly losing energy, her angle of attack increasing toward the stall. In Pitch Alternate Roll Direct Law the pilot's back pressure on the sidestick was also moving the powerful Trimmable Horizontal Stabilizer, moving it slowly to full nose-up, effectively locking them into the stall that would follow momentarily.

Today David Learmount of Flight Global posted a blog titled Being an airline pilot isA profession in decline”. Is it really? He quotes from William Langewiesche's book Fly by Wire, citing Langewiesche's admiration for Bernard Ziegler and the Airbus and his ambivalent attitude toward airline pilots. I will add another quote from the book:

“What did Ziegler want? He wanted to build an airplane that could not be stalled – not once, not ever – by any pilot at the controls.”

She fell flat, nose and wings level with the horizon, falling not flying, her angle of attack near ninety degrees, her rate of descent 10,000 feet per minute. Four minutes later she hit the water.

Nemesis and Lesson

Here is another quote from Fly by Wire:

“If you design airplanes for (airline pilots) to fly, you must grapple with not only with the existence of a few who are incompetent from the start, but also with the fact that plenty of once-excellent pilots grow unsafe with time. They become arrogant, bored, or complacent. They drink, they fade, they erode.”

Bernard Ziegler is (was) a brilliant test pilot and engineer. (Like me, he is getting older.) He knew that he was on the far right flare of the bell curve. He knew (as do we all) some examples from the left rim of the bell.

I am from somewhere in the middle of the curve. I was lucky, worked hard to maintain my competence, and survived my job. I don't dispute the factuality of the above quote. But I would add a caution:

Underestimate a tradesperson at your own risk.

Chesley Sullenberger knew his airplane, respected her and treated her like an equal. He expected Jeffrey Skiles to act professionally and he did. He was proud of his profession, his trade. That was his true achievement. The successful ditching followed from it, a corollary.

David P. Davies gets it right-way-around in his classic Handling the Big Jets:

“Airline flying is just money for old rope most of the time . . .”

He recognizes, as pilots say, that flying is hours of boredom punctuated by moments of sheer terror.

But he also points out the need for training of the highest quality. That designing an airplane that is capable of landing safely with half its engines failed is of no use if you haven't trained the pilots to do the maneuver. If you haven't given them the confidence that they can.

So pilots: know your airplane. Treat her and your fellow-pilots well. Expect the best from them.

And to everyone, especially homeowners: respect tradespeople. Search out those who are proud of their work. Especially if you're looking for a roofer.