TNAG-2856-FCO40-4109-Hong-Kong-compensation-claim-regarding-Korean-Air-Lines-Flig-1993 — Page 127

- 56 -

2.17

The possibility of instrument failure

2.17.1

The flight crew of KE 007 did not report any problem, call for assistance, or indicate in any way that they were unable to comply with the navigational requirements of their assigned route. The fact that no difficulties were reported and that the flight crew provided position reports and forward estimates, and reported spot winds indicated that at least two of the INS systems were functioning normally. The aircraft departed Anchorage with a defect to the No. 2 compass system, which was deferred for rectification in Seoul. There remained four heading reference systems as well as the standby compass. There was no indication of an in-flight failure in the aircraft's instrumentation or navigation systems.

2.17.2

The CVR record of conversation on the flight deck and with KE 015 did not include any indication of an instrument failure or problems with navigation. At 18:05 hours the two crews discussed the anomaly of each aircraft experiencing different winds in what they believed to be the same vicinity and again there was no reference to navigation difficulties being experienced by KE 007.

2.18

2.18.1

The inertial navigation system

The flight crew used the autopilot in the heading select mode to fly a selected heading towards Bethel VORTAC before the aircraft was within the range of that facility. If subsequently, they either did not select the navigation mode switch to INS or made such a selection when the aircraft was outside the 7.5 NM envelope for the capture of a desired INS track and was flying away from that track, then the aircraft would have continued on the magnetic heading selected previously.

2.18.2

In the above situations the INS CDUs would have displayed the alert light as was normal prior to waypoint passage, and would have indicated waypoint passage when the aircraft passed abeam of the waypoint position. The indications to the crew that they were not making good the programmed waypoints would have included:

a) at waypoint passage the present position co-ordinates would have

differed from those of the desired position;

b) the cross-track error would have progressively increased and would have become unacceptable at BETHEL and at the waypoints thereafter;

c) the distance to go to the waypoint when the alert light began flashing

would not have been reconcilable with the time to go;

d) depending upon the selection of the VOR/ILS and INS switch, the captain's and/or the first officer's HSI would have indicated a maximum deviation from the desired track at BETHEL and thereafter;

e) the correct indications for the INS controlled automatic flight would not have been displayed on the flight director and autopilot mode annunciator panels; and