Singapore Airlines, B747-400, Primary Flight Display information loss, 23 January 2003

Synopsis A Boeing 747-400 lost all information on its six electronic display units in cruise from Singapore to Sydney. Loss of primary flight data is a critical incident; aircraft have standby (backup) instruments, which rely on completely separate system components to avoid common-cause failure. The crew flew the aircraft using the standby flight data instrumentation while they trouble-shot the problem. Cycling the circuit breakers for the EFIS/EICAS interface units restored the electronic display units to normal operation.

On 2 December, 2003, the U.S. National Transportation Safety Board issued Recommendations A-03-55 and A-03-56. The short document may be read at www.ntsb.gov/Recs/letters/2003/A03_55_56.pdf. The note recounts the incident as follows:

On January 23, 2003, a Singapore Airlines (SIA) Boeing 747-400 experienced a complete loss of information on all six integrated display units (IDU) on the flight deck instrument panels while in cruise flight from Singapore to Sydney, Australia. The pilots flew the airplane for 45 minutes using standby flight instruments while they communicated with SIA maintenance personnel about the problem. SIA maintenance personnel advised the flight crew to pull out then push back in (or cycle) the circuit breakers for the EFIS/EICAS interface units (EIU), which returned the IDUs to normal operation. The flight continued to Sydney and landed without further incident.

A similar event occurred on another SIA B747-400 on November 6, 2001 ...

This earlier event occured to a Sydney-to-Singapore flight, during an emergency descent because of an cabin pressure warning. Maintenance personnel recycled the EIU circuit breakers on the ground and restored the IDUs to normal operation.

The six IDUs ... include the captain's Primary Flight Display (PFD) and Navigation Display (ND), the first officer's PFD and ND, and the main and auxiliary engine indicating and crew alerting system (EICAS) displays. The PFD and ND displays [sic] provide the pilots with attitude, altitude, airspeed, heading, and rate of climb and descent information. The EICAS displays provide the flight crew with the airplane's engine indicating information and annunciate advisories, cautions and warnings. Without these displays, the flight crew is required to use standby flight instruments, which consist of an altimeter, airspeed indicator, and artificial horizon/attitude indicator; the Boeing B747-400 does not have standby engine instruments. The loss of the IDUs would also eliminate the flight crew's access to data from the traffic alert and collision avoidance system, enhanced ground proximity warning system, and weather radar.

The EIUs are apparently responsible for data display on all six IDUs and preliminary investigation has indicated that all six IDUs blanked because all three EIUs stopped transmitting data. The EIUs are identical devices; the architecture is triple-redundant. The cause of this loss of data has not been determined, and no countermeasures have yet been identified that could inhibit the loss of all six IDUs again.

Boeing recommended cycling the EIU circuit breakers in such an event, and the NTSB recommended that this procedure be included in the quick-reference handbook used by the flight crew to access procedures in an emergency.

The NTSB letter was also reported in Flight International, 9-15 December 2003, p13; and by Frances Fiorino on p31 of Aviation Week and Space Technology, December 15, 2003.

I recounted this incident, in much the same words as here, in an article B747-400 Electronic flight displays rendered inoperative in the Risks Digest, Volume 23 Number 12, 12 January, 2004.