A Public TV “Frontline” episode this evening was devoted to the crash of Colgan 3407. After my one-year FiOS deal ran out and they presented me with a shocking monthly bill, I canceled cable but the program is available streaming online.
The TV show was notable mostly for how much time it is possible to waste by watching TV. In a full hour of human life, one learns that it sucks to get paid $20,000 per year and work 16-hour days. We don’t learn anything about why the airplane crashed, except that the hero Captain Sully would not have crashed it.
Who crashed Colgan 3407? Actually the autopilot did. The crew told the autopilot to level the plane, but left the throttles back near idle. This caused a gradual speed decay. Then the pilots extended flaps and gear, resulting in a big increase in drag. They should have added power at this point, but did not. Acting less competently than the typical person on his very first flight lesson, the autopilot kept pulling the nose up in an attempt to hold altitude. Eventually it pulled the airplane past the “maximum lift/drag” speed in which it would hold the most altitude for a given power. And then it kept pulling until the airplane was just about stalled. And then it disconnected, dumping the trimmed-to-crash airplane into the laps of the sick and tired human pilots. Seconds later, everyone was doomed. See the NTSB animation of the flight.
The airplane had all of the information necessary to prevent this crash. The airspeed was available in digital form. The power setting was available in digital form. The status of the landing gear was available in digital form. The airplane had the ability to put synthetic voice announcements into the pilots’ headsets. Here’s what you’d expect to happen:
- autopilot is set to descend and then level off and hold altitude at 2300′
- human pilots neglect to push throttles forward
- after a few seconds, autopilot annunciates “leveled off but throttles are still at idle”
- pilots put landing gear down; speed decays very quickly
- autopilot annunciates “more power required to hold altitude and airspeed”
- speed decays below 1.3 times the stall speed
- autopilot stops trimming back and says, this time in a very sharp and loud voice “holding 160 knots, descending out of 2300′ due to inadequate power”
How come the autopilot software on this $27 million airplane wasn’t smart enough to fly basically sensible attitudes and airspeeds? Partly because FAA certification requirements make it prohibitively expensive to develop software or electronics that go into certified aircraft. It can literally cost $1 million to make a minor change. Sometimes the government protecting us from small risks exposes us to much bigger ones.
As many bricks as people are hurling at the memories of the crew of Colgan 3407, they probably would have landed safely in Buffalo if no autopilot had been installed in that airplane. Sometimes a really stupid autopilot is worse than none.
[As far as I know, Airbuses are the only airplanes that are any smarter than the Bombardier Dash 8 flown by the Colgan crew (see my Fly by Wire review). There is a glimmer of hope in the small airplane world, however. The new Avidyne autopilots incorporate “flight envelope protection”, which will put these $10,000 machines many years ahead of the competition (if the FAA ever certifies them).]