A US reader has found an intriguing report into an incident in 1996 in which an American Airlines Airbus A300-600R suffered from some of the issues identified as affecting AF447 .
The jet flew into severe icing conditions and the pilots lost reliable speed readings.
This jet pre dates the fly-by-wire and intensively computer aided control management systems found in all current Airbus airliners, and the A330-200 lost on 1 June in the mid Atlantic .
The report has been largely been de-jargonised, and refers to an American Airlines flight from JFK to a Caribbean destination.
Narrative
While climbing at 28,000 feet all airspeed and altitude information was lost for approximately 10-15 mins.
While attempting to level off could not pull back #2 throttle. It was physically stuck at approx max climb power . Flight experienced buffeting. Pilots suspected high speed buffeting but could have been low spd. retarded #1 throttle and buffet stopped. Made normal landing after all conditions returned to normal.
The pitot static heat was on and appeared to be working normally.
Subsequent information was that the pilot in command heard from his maintenance division that there was water in the pitot static lines.
Why the water was in the lines is unknown, but the mechanic said, ‘the conditions were just right.’ The A300 has triple redundant airspeed readings, two digital with display on the Pilot Flight Display, and 1 analog gauge, and they were all affected.
The pilots first noticed the analog gauge reading 0 knots, then the digital displays on the PFD started fluctuating +/-10 knots. Shortly the analog spds were fluctuating from minimum to max on the gauge and the digital spd going from ‘green dot’ to red line maximum. At the same time the altimeter was frozen. They noticed their airspeeds decrease to green dot, the minimum maneuvering speed, and weren’t sure what the speed actually was because of all the erroneous info. To be safe, they decided to descend to insure the airspeed was not actually slow, and as they pushed the nose over the altimeter didn’t respond at all.
Shortly they got a buffet and the Captain identified it as high speed, rather than low speed, and the nav display showed 460 knots. They asked air traffic control what speed they were reading and the reply was 430 knots. Part of the speed increase was the inability to pull the #2 throttle back and it stayed at climb power temporarily. They were able to overcome the stuck throttle, however, and it appeared normal for the rest of the flight.Feedback from maintenance says that the stuck throttle is not uncommon on that aircraft. The suspected cause of the stiff, unmoveable throttle, was the shroud cover which surrounds the throttle cable which sometimes gets a heat build up which in turn melts the shroud and thus restricts the cable. The flight crew was very concerned with the chain of events and both say it was the scariest moment in their flying careers. They had multiple failures of critical flight instruments and were not sure what they had or what was accurate and what wasn’t. Once out of the clouds the problems cleared up, and because the weather was a lot better at their destination than at closer airports, they chose to continue. The rest of the flight was uneventful.
Synopsis
Since all airspeeds and altitude information was unreliable, it would seem logical that the common thread was the pitot static system, and specifically, ice. The pitot heat was on and appeared to be operating normally. When they flew out of the cloudy conditions, all systems again were normal.
What this report has in common with a string of similar incidents involving the more modern A330 is that the pilots applied the operating procedures for dealing with the unreliable air speed indications. It doesn’t tell us that current computer aided flight control management systems are inherently less safe than those of earlier generation airliners at all.
Nor does it allow the conclusion that the Air France jet was not flown professionally.
It is however a reminder that something additional took place on AF447, and finding out what that was may prove impossible without locating and recovering the two black box flight recorders from the under sea mountain ranges that lie thousands of metres below the crash zone.
