TNAG-2856-FCO40-4109-Hong-Kong-compensation-claim-regarding-Korean-Air-Lines-Flig-1993 — Page 113

- 42 -

2.4

2.4.1

Navigation to Bethel VORTAC

Anchorage VOR/DME had been out of service since 23 August 1983. The clearance. given indicated that the normal means for ensuring navigation on route J501 west of Anchorage VOR/DME was not available.

2.4.2

There were two ways of using the INS to navigate to Bethel VORTAC with autopilot A already in use. Selection of the navigation mode switch to INS would have initiated the INS navigation mode to capture the desired INS track from the Anchorage VOR/DME (waypoint 1) to Cairn Mountain NDB (waypoint 2), provided that the aircraft was both west of the Anchorage VOR/DME_and_within 7.5 NM of the desired track. The flight director and the autopilot annunciator panels would have indicated that the NAV mode was in operation in each case. Had the aircraft been displaced more than 7.5 NM from the desired track the flight director and auto-pilot annunciator panels would have indicated. that the INS NAV modes had armed but not come into operation. In that case the flight director and the autopilot mode annunciator panels would have indicated that the NAV modes were armed until the aircraft was within 7.5 NM of the desired track when both would have indicated that the INS NAV modes were in operation. The fact that the heading modes of the flight director and autopilot would have been in operation during the armed phase of the INS navigation modes would not have been indicated.

2.4.3

Alternatively, a similar selection of INS on the navigation mode switch followed by a selection of track change 0 to 3 on the No. 1 INS CDU would have initiated the INS navigation mode from the position at the time of the selection (waypoint 0) to BETHEL (waypoint 3). The flight director and autopilot mode annunciators would have indicated that the INS NAV modes were in operation. This track change would then have been made on the No. 2 and No. 3 INS CDUs.

2.4.4

In either of these cases the aircraft would have been expected to navigate to BETHEL with no or very little error. Either would have resulted in some small alterations in magnetic heading as the INS achieved the true track towards BETHEL. Indications available to the crew would have been a reducing or zero track bar displacement with the HSI display set to INS and a similar reducing or zero cross-track error on the CDUs. There would have been a similar effect with the VOR track displacement subsequent to receipt of Bethel VORTAC if the VOR/ILS display had been selected on the HSI.

2.5

Constant magnetic heading

2.5.1

The navigation mode switch was selected to HDG for take-off. The DFDR record indicated that an appropriate heading towards Bethel VORTAC was then selected. If the navigation mode switch was left in the HDG position, then the aircraft would have maintained the heading selected. Neither the flight director nor the autopilot annunciator panels would have indicated that the heading modes were in operation.

2.5.2

Alternatively, had the navigation mode switch been selected to INS outside the INS desired track capture envelope and had a closing heading not been selected the flight director and autopilot NAV modes would have been armed, and would have remained armed so long as this condition persisted, whilst the heading modes would have remained in operation. The flight director and the autopilot annunciator panels would have indicated that the INS navigation modes were armed but there would have been no direct indication that the systems were operating in the heading modes.