Narrative:

We were on course, all system normal when we noticed multiple aircraft system failures. The captain's RMI compass flag appeared with no other flags in view, neither on the captain's HSI nor the copilot's RMI or HSI. There were no other cockpit instrument warnings of this condition, either by audio or visibility means. The captain selected #2 compass system and the flag disappeared. A comparison of both mach speed indicators were vastly desperate with reading differences between .25 to .65. INS failures in all INS's indicated by a no wind readout condition in both #1 and #3 units with all 3 units indicating different drift angles and different crosstrack #'south. Note #3 failure between vhhh and rjaa and was changed in rjaa. Instant and steadying altimeter readings with differences of 400' when using corrected altimeter. When captain's altimeter was selected to standby the altimeters' readings agreed. All these problems led us to believe there was at least one CADC failure with system #1. Later we noticed 'a' autoplt had tripped to manual, and we felt that we were off course and therefore made a course correction and resumed trying to analyze and correct the multiple system failures. We reached onade 68.6 NM on the 328 degrees from the shemya VOR. Upon landing we wrote up most of the failures. A ftl captain's irregularity report was submitted in 4/89. Recommendations to preclude a similar incident or worse, a catastrophic accident are as follows: first we need to recognize that we fly different models of same type and that they are wired differently. The problem originated when we switched to #2 compass system and were unaware that the autoplt had tripped to manual. Switching compass system does not trip the autoplt to manual in most of our aircraft. Cost may preclude rewiring older aircraft to the later specifications, but rewiring would be the preferable way. Alternately our training program should stress this type of difference between aircraft. There are several reasons that will trip the autoplt to manual, but switching compass system is not listed as one of the methods in the widebody transport flight manual. Even when the autoplt has been tripped for one of the listed reasons, it has gone unnoticed for periods of time after the trip. There should be an autoplt warning for a trip to manual. A light warning would be adequate. When we disconnect the autoplt intentionally we get both an audio and visibility warning, why not for a trip to manual?

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Original NASA ASRS Text

Title: ACR WDB TRACK DEVIATION. FLT CREW FAILED TO NOTICE THAT THE AUTOPLT HAD SWITCHED FROM COMMAND TO MANUAL MODE WHEN THEY ACTIVATED COMPASS TRANSFER SWITCH.

Narrative: WE WERE ON COURSE, ALL SYS NORMAL WHEN WE NOTICED MULTIPLE ACFT SYS FAILURES. THE CAPT'S RMI COMPASS FLAG APPEARED WITH NO OTHER FLAGS IN VIEW, NEITHER ON THE CAPT'S HSI NOR THE COPLT'S RMI OR HSI. THERE WERE NO OTHER COCKPIT INST WARNINGS OF THIS CONDITION, EITHER BY AUDIO OR VIS MEANS. THE CAPT SELECTED #2 COMPASS SYS AND THE FLAG DISAPPEARED. A COMPARISON OF BOTH MACH SPD INDICATORS WERE VASTLY DESPERATE WITH READING DIFFERENCES BTWN .25 TO .65. INS FAILURES IN ALL INS'S INDICATED BY A NO WIND READOUT CONDITION IN BOTH #1 AND #3 UNITS WITH ALL 3 UNITS INDICATING DIFFERENT DRIFT ANGLES AND DIFFERENT CROSSTRACK #'S. NOTE #3 FAILURE BTWN VHHH AND RJAA AND WAS CHANGED IN RJAA. INSTANT AND STEADYING ALTIMETER READINGS WITH DIFFERENCES OF 400' WHEN USING CORRECTED ALTIMETER. WHEN CAPT'S ALTIMETER WAS SELECTED TO STANDBY THE ALTIMETERS' READINGS AGREED. ALL THESE PROBS LED US TO BELIEVE THERE WAS AT LEAST ONE CADC FAILURE WITH SYS #1. LATER WE NOTICED 'A' AUTOPLT HAD TRIPPED TO MANUAL, AND WE FELT THAT WE WERE OFF COURSE AND THEREFORE MADE A COURSE CORRECTION AND RESUMED TRYING TO ANALYZE AND CORRECT THE MULTIPLE SYS FAILURES. WE REACHED ONADE 68.6 NM ON THE 328 DEGS FROM THE SHEMYA VOR. UPON LNDG WE WROTE UP MOST OF THE FAILURES. A FTL CAPT'S IRREGULARITY RPT WAS SUBMITTED IN 4/89. RECOMMENDATIONS TO PRECLUDE A SIMILAR INCIDENT OR WORSE, A CATASTROPHIC ACCIDENT ARE AS FOLLOWS: FIRST WE NEED TO RECOGNIZE THAT WE FLY DIFFERENT MODELS OF SAME TYPE AND THAT THEY ARE WIRED DIFFERENTLY. THE PROB ORIGINATED WHEN WE SWITCHED TO #2 COMPASS SYS AND WERE UNAWARE THAT THE AUTOPLT HAD TRIPPED TO MANUAL. SWITCHING COMPASS SYS DOES NOT TRIP THE AUTOPLT TO MANUAL IN MOST OF OUR ACFT. COST MAY PRECLUDE REWIRING OLDER ACFT TO THE LATER SPECS, BUT REWIRING WOULD BE THE PREFERABLE WAY. ALTERNATELY OUR TRNING PROGRAM SHOULD STRESS THIS TYPE OF DIFFERENCE BTWN ACFT. THERE ARE SEVERAL REASONS THAT WILL TRIP THE AUTOPLT TO MANUAL, BUT SWITCHING COMPASS SYS IS NOT LISTED AS ONE OF THE METHODS IN THE WDB FLT MANUAL. EVEN WHEN THE AUTOPLT HAS BEEN TRIPPED FOR ONE OF THE LISTED REASONS, IT HAS GONE UNNOTICED FOR PERIODS OF TIME AFTER THE TRIP. THERE SHOULD BE AN AUTOPLT WARNING FOR A TRIP TO MANUAL. A LIGHT WARNING WOULD BE ADEQUATE. WHEN WE DISCONNECT THE AUTOPLT INTENTIONALLY WE GET BOTH AN AUDIO AND VIS WARNING, WHY NOT FOR A TRIP TO MANUAL?

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.