A Simple System with Profound Consequences

Among the many programs I have been watching on Amazon Prime and Netflix is a short series on airliner crashes over the years, with detailed explanations as to the causes. Actually in checking imdb, there have been many seasons but Amazon has just the first.

The accident investigators are interviewed, the controllers, and sometimes the passengers. I’ve seen 3 or 4 episodes, and it has been illuminating, not only for the causes but the pressures from the airline industry (which is understandable, given their investments). I’m thinking of the episode detailing the United Airlines 747, flight 811,  that had the cargo hold door explode from pressure over the Pacific.

It was eventually determined to be a faulty design in the latch, and the FAA mandated that it be updated. Parts were only $2,000 (amazing for the aircraft industry!), but the downtime just for that sidelining these jets (that are only making money when they are flying, making money so they can pay off the lease or loans), would run into many millions. So the airlines lobbied the FAA to allow them to wait until a major inspection when the planes would be offline anyway.

When a separate incident occurred, the FAA sped up the requirement. Not condoning the longer wait request, but can certainly understand it in the context of economics.

Although in the case of United 811, the flight crew, through superb flying (2 of the engines were out due to the debris) , brought it back to Honolulu although 9 passengers lost their lives being blown out of the damaged fuselage.

Take a look at the damage.

Anyway in the episode I just finished, they were talking about  Aero Peru 757 Flight 603 that, 5 minutes after takeoff, noticed a complete failure of all the primary flight instruments. They had no idea of their airspeed or altitude. And it was all traced to a stupid maintenance error.

Spoiler Alert 

When cleaning the airplane, the maintenance crew put duct tape over the static holes (part of the pitot-static system) while they washed the plane. But despite an institutional arrangement where 3 people (starting with the supervisor and ending with the captain doing a pre-flight), all missed the tape. Because duct tape is silver, and the holes on the wing were 15-17′ up – and it was night, all missed it.

And because in modern airliners so much computerization is dependent on this simple design, a design that has been around since at least the 1920s, there was pandemonium in the cockpit between the Captain and First Officer.

Imagine being over the ocean at night, with no visual references as to the horizon or the surface, and the computers are screaming to you that you are first going too fast then on the verge of stalling.  And for the final nail, the controller at Lima is verifying the altitude that their faulty altimeters are giving – not thinking that the plane’s transponder was simply transmitting that erroneous information. He was giving back the same bad information.

The 757 eventually flew into the dark Pacific.

Imagine being in that situation as at least 2 other flight crews faced.

In the case of the Birgenair, it was most likely a wasp nest in the pitot tube that the maintenance crew missed. In Air France 447, it was an iced over pitot tube.

Lex had a (naturally) good post on AF 447.

In the episode, a retired Canadian 757 Captain talks about what he would have done.

Easy, I suppose, to see “what they should have done” given the fact that we know what happened, but imagine the confusion when it is pitch black and multiple systems are blaring at you about critical failures.

Aviate – Navigate – Communicate – in that order.


05-28-20 In re-reading this, I was reminded of a book on survival I reviewed here some time ago. I found it fascinating, for the real-world examples the author gave of some – who with their experience and physical conditioning – should have survived their situations while others seemed to survive against improbable odds.

I’m thinking of a 16 year old girl who, in a dress, survived an airliner crash in the Peruvian jungle and for some days walked through that jungle until she saw a village. She was the sole survivor – the other survivors of the crash decided to wait for help.

She remembered something her father said about water – to “follow the streams – it will eventually lead you to people”.

The takeaway point from this book?

Stop for a moment – access the situation. Make a plan. 

In all three of these instances above – the flight crews were reacting to the false instrument readings and in essence – “bouncing off the walls”. 

What the Canadian pilot said in the program was the same as what Lex said about AF 447 – that you know the throttle lever position for cruise – put it there and with the engines running (you have good instruments telling you their state), you know that you are at cruising speed.

No matter what your airspeed indicator or altimeter tells you.

1 Comment

Filed under Aeronautical Engineering, Flying

One response to “A Simple System with Profound Consequences

  1. Pingback: Aviation – When to Listen to the Computer | The Lexicans

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