United Airlines discovered they missed a deadline to complete a required maintenance directive on their fleet of 96 Boeing 757-200 aircraft yesterday, causing some cancellations and significant delays. It is being reported that between 7 and 17 flights were cancelled yesterday, and delays could trickle through into today.

The Federal Airworthiness Directive in question was issued in May of 2004, and required “modification of the air data computer (ADC) system, which involves installing certain new circuit breakers, relays, and related components, and making various wiring changes in and between the flight deck and main equipment center.†It is necessary to allow the pilots to silence automatic audible warning commands that were made in error noting (incorrectly) that the maximum airspeed was being exceeded, or the aircraft was about to stall. It sounds to me, though, that there should be a deeper level fix, namely making sure those erroneous warnings don’t occur in the first place. In any case, the airline had between 24- and 72 months from the effective date of June 22, 2004 to complete the work. That would have been in June 2006 through June 2007 timeframe, so while it is a major FAIL for United, I will give them credit for doing the right thing and taking immediate action by temporarily grounding the fleet. It is unclear at this point what action the FAA will take against United for this mistake.

United’s premium and high-yield Los Angeles/San Francisco to New York market is served exclusively by the 757, and the afternoon bank of flights saw significant delays. The 2:05pm departure from LAX to JFK didn’t leave until 6:35pm, with an arrival in New York at 2:23am. The next departure left nearly 3 hours late, and the red-eye at 10:55pm had a one-hour delay. Flights this morning appear to be mostly on-time, although delays are still possible.