Originally Posted by
Airbubba
It looks like FR24 had six receivers near MDE that could provide multilateration location data on playback. Some of the other flights depicted on the playback animation seem to be MLAT only with occasional position shifts due to terrain and receiver geometry.
I think FR24 will default to displaying ADS-B data when it's available. I'm wondering if MLAT data for LMI2933 is available somewhere in the FR24 database for comparison to the transmitted ADS-B track.
Were the pilots of the RJ85 seeing a map display updated by radio navaids while the ADS-B was sending inertial only data?
Or, was the cockpit nav display also showing the wrong shifted position for some reason? The fact that the plane crashed so close to the VOR instead of the runway threshold makes me wonder.
It would not take too many MLAT measurement to rule out an 8 nm error in the FR24 reports, which I believe to represent raw IRS 1 position.
I dwelled a lot in the blog on how the GNS-X computes composite position for LNAV, and how this could be a factor (map shift?) in leading the flight crew to believe they were operating much closer to MDE than they may have been. But this is just a convenient explanation, I don't have anything to say that is what happened.
The descent captured to the last reported position (FR24) aligned (with a reasonable offset) to the final resting place, both in range and bearing.
The transponders are lost with EMERG AC/DC. As is EFIS. And DME. The crew would resort to LOC on the standby Attitude Indicator and VOR on the DBI, neither of which would reveal the displaced position since they were flying along a line (the VOR cross-over would be noted). They were above the G/S until after flameout.
If the FR24 data was wrong, that LMI2933 was operating much closer to the airport than recorded, than the final resting place does not add up assuming a controlled descent generally northbound. It would imply something like a 5,000 fpm descent rate which makes time aloft a question too (need to look into that from the transcript). Another option is a circling descent, but again that does not seem consistent with the pilot reports.
The glide ratio (flaps up or flaps down, gear ***DOWN***) is 1 nm per 1,000 feet (6:1). It is arguable what the descent rate would be for flaps down, assuming both are flown at best glide speed. They lost engines about 8,000 above the runway, which means they should have been able to glide some distance (8 nm?). I was assuming a V/S of about 2,500 fpm would yield about three minutes of flight at about 140 KTAS or about 7 nm.
Glide Ratio (Flaps Up, Gear up) is 2.5 nm per 1,000 feet.p (15:1).
The SSR data will resolve this point, and maybe the flight data recorder will offer some insights.