Originally Posted by
Icelanta
For some reason, IF date from FR24 is correct, the aircraft was flying a "phantom. ILS" around 4km. Offset to the West.
Now there is only one way I see this happening, and that would imply a total lack of procedures, and I will not put this on a public forum.
Originally Posted by
scanelpan
My question: would it be possible to program the FMCs to perform a LNAV/VNAV approach with RW26 as active runway, but with final descent waypoint (mistakably) threshold RW08? I could not think of a good reason to use such a construction under the prevailing conditions, so I want to emphasize, its a technical question only.
Originally Posted by
Icelanta
Scanelpan,
Yes, this is possible, and to be honest, I have already thought about this.
But surely no sane crew would do this...
Originally Posted by
Machinbird
Would it be possible for this accident aircraft to set up an approach to the wrong end of the runway by keying in the wrong data? It wouldn't be a full ILS of course, but might use a combination of GPS and localizer data.
Originally Posted by
despegue
Regarding the possibility of setting-up a manual inserted approach into the fmc, let me give this theoretical possibility:
crew initially planned for an approach on rwy08, which is logical as this would be the preferential rwy according to current wind in the metar/atis, and had to change last minute for a setup for rwy26.
Runway and/or approach not in fmc database, manual entries in fmc. This caused the crew to be rushed.
As the aircraft showed problems with capturing ILS signals on previous sectors, which was not put in the techlog, (something that is a common occurence with ACT by the way), they followed a LNAV/VNAV approach, with a vnav path based on last point in fmc: threshold rwy08 where VNAV calculates to fly over at 50' .
This is by the way a rumour "on the ground"...
Totally unbelieveable obviously, but theoretically possible and an explanation that correlates with current information.
The late runway switch scenario has set up a chain of events leading to a mishap many times in the FMS era. The 1995 American Cali crash and 2013 UPS crash at Birmingham are two examples that come to mind.
I've done the FMS drill of extending off a runway to build an advisory path for a visual landing on Boeing twins but I agree with everyone else that this would be suicidal in low vis to CAT II mins even if you did it right.
For the B-744 drivers, is it possible to select runway 08 and build a path in the wrong direction as some of the speculation implies? Doesn't the RW08 waypoint know the heading and plot a centerline on the ND? Or, can you just do an intercept to RW08 with an inbound course of 260 and a 3.0 degree path angle? Would LNAV and VNAV capture in this 'backwards' setup with a runway waypoint?
On some of the boxes I've flown with I don't think you can change the inbound course to a runway waypoint, i.e. go straight to the 'numbers', you have to do an intercept to a waypoint on the final course (e.g. RW08/-2). The idea is to prevent the path to the wrong end of the runway error on a 'homebuilt' approach.
Or, did they build an
ad hoc approach using the wrong NDB?
Originally Posted by
klintE
Yes. But NDB for RWY08 is situated almost exactly where they crashed. Suppose this is just coincidence (no irony)