Safety Case Studies

Safety Case Studies examines aviation incidents and accidents that involved maintenance as either a probable cause or as a factor. The cases are culled from the National Transportation Safety Board database, from news reports, and from foreign accident investigation bureaus.

SHADES OF THE ROSELAWN CRASH

Unlike the American Eagle ATR-72 that fatally crashed at Roselawn, Ind., in 1994 from inflight icing, the captain of an American Eagle Saab 340 was able to recover the airplane after encountering icing conditions on January 2 and land at Los Angeles International Airport without injury to his crew or 25 passengers. From the NTSB preliminary report, issued pursuant to an investigation, are tantalizing bits about the upset/recovery and maintenance aspects of the case:

"The captain began to reach up to activate the manual deice boot system and the airplane vibrated. The airplane encountered ice and the windscreen immediately turned white. The clacker and stick-shaker activated and the captain took control of the airplane. The autopilot disengaged and the airplane began to bank left in a nose low attitude. The airplane began a rapid descent and the captain recovered at an altitude of about 6,500 feet [the upset occurred at about 11,500 feet].

"National Transportation Safety Board investigators reviewed the airplane's maintenance records and logbooks. The day prior to the incident a flight crew reported that during an en route deice boot check, the timer light illuminated. The deicer timer failure light was later deferred in accordance with the operator's minimum equipment list (MEL). The deferral procedures required a placard to be placed adjacent to the deicer timer switch and the auto cycling switch to remain in the `off' position. An MEL placard (sticker) was next to the deice system controls in the cockpit.

"Initial examinations revealed the airplane's deice systems were operational; however, the deicer timer failure light illuminated. The investigation is ongoing."

The question becomes whether or not manual de-icing actuation is a safe option once the timer is in failure mode. The answer at this stage would appear to be "no." (NTSB report: www.ntsb.gov/ntsb/brief.asp?ev_id=20060109X00033&key=1)

THE OPPOSITE OF WHAT WAS INTENDED

The pilot-in-command reported that "the control forces required to maintain straight and level flight were very high and fatiguing" on the Fairchild Metro 23 regional aircraft in the August 2, 2004 incident. According to the final report by the Australian Transport Safety Bureau (ATSB), released January 3, a subsequent engineering examination revealed that the pilot's control yoke pitch trim switch had been wired incorrectly and "was operating in the reverse sense from normal operation."

According to the ATSB report:

"Prior to the incident, the aircraft had undergone maintenance for the flight controls being heavy in the roll (aileron) axis. The problem was traced to a binding bearing in the left side control yoke ... After the control column bearings were replaced, the control yoke was re-installed and the trim switch wiring was re-soldered to the respective terminals. During this task, the wiring labeling was misread and the trim switch wires were inadvertently transposed, which would result in the trim switch operating in the reverse sense when activated ...

"During the aircraft maintenance activity, there were a number of different maintenance engineers involved over several shifts. The handover between shifts was completed [but] details of the aircraft's pitch trim system wiring information was not referred to the incoming shift engineers through the handover book. ...

"An examination of the aircraft maintenance records indicated that two duplicate inspections were omitted, including one for the left side control yoke wiring reconnection."

The issue is whether it's acceptable to test-fly an aircraft on a revenue operation after work on flight controls. (ATSB report: www.atsb.gov.au/publications/investigation_reports/2004/AAIR/aair200402839.aspx)

TAKEOFF FROM LONDON HEATHROW AND LANDING AT LONDON GATWICK

"The investigation determined that the incident [left roll control needed to prevent the B757 from turning right, and hot oil smell in cockpit] had been caused by maintenance errors that had culminated in the failure to reinstall two access panels ... on the right-hand outboard flap and incorrect procedures being used to service the engine oils," according to a UK Air Accidents Investigation Branch (AAIB) report (No. 3/2005), released December 14, 2005, concerning the British Airways jet and its first flight in September 2003 following a 26-day major maintenance check.

The AAIB report noted that, "Ineffective supervision of maintenance staff had allowed working practices to develop that had compromised the level of airworthiness control and had become accepted as the `norm.' " There are 35 findings and 8 recommendations in the report. Some of the findings will give a flavor for the report's recommendation for, inter alia, better oversight: