Carrier Acts to Assure Its Pilots the 737 is Safe

Air Safety Week, April 19, 1999

DAYTONA BEACH, Fla. - Pilot concerns over the safety and reliability of the B737 rudder control system have been serious enough to prompt one airline to issue a written assurance.

In the wake of the March 23-24 hearing by the National Transportation Safety Board (NTSB) into two crashes and one incident in which errant rudder deflections were deemed the cause, pilots with United Airlines [UAL] have reacted by reporting anything and everything they regard as a possible rudder anomaly.

There have been at least one aborted takeoff and three returns to the departure airfield since the NTSB hearing. Capt. Edmund Soliday, United's VP of safety and security, told attendees at a Society of Automotive Engineers (SAE) aviation safety conference here that "I'm looking at a flight recorder readout every two days now" on 737 rudders.

"When the solution is fuzzy, the pilots are responding to anything they sense as an anomaly," Soliday said. The activity is a natural result of a high-profile investigation, Soliday said, and he expects the pilot concerns to abate "in about another week."

In the meantime, the carrier has issued a flight safety bulletin to assure its pilots that modifications to the rudder control system are well in hand, and that the NTSB's investigation into the fatal 1994 USAir flight 427 crash near Pittsburgh, and the fatal 1991 United Flight 585 crash at Colorado Springs "have revealed valuable safety information" which have stimulated changes "to enhance the already exceptional safety record of the B737."

The United bulletin also challenged the "questionable validity" of the NTSB's dramatic animation of the final moments of Flight 585, which investigators presented at the hearing last month to illustrate the sudden impact of an uncommanded rudder reversal. >> Soliday, tel. 847/700-4224 <<

Challenging the Computer Simulation of the 1991 Crash of United Flight 585

"The NTSB reported that new computer simulation technologies developed for the USAir investigation may provide further insight into our 1991 crash. It was our opinion that the computer simulation study was an effort by the NTSB to prove their theory that a rudder reversal was the cause of the USAir and United accidents, and an Eastwind Airlines recovered upset...

"We believed there was a lack of sufficiently accurate baseline data from which to program such simulations because the flight data recorder on the Colorado Springs' airplane recorded only 4 flight parameters - each with a margin of error which could substantially effect the results of the simulation. Even the NTSB's final factual report...questioned whether the computer simulation could define a unique solution for the United upset.

"While United recognizes the potential for the use of simulations to enhance future investigations we question the validity of the simulation results and reject any suggestion that such a simulation was able to identify a cause in United's Colorado Springs accident."

Source: United Airlines Flight Safety Information Bulletin 99-3