passenger flight information.

[witwiw]

Does anyone know the source of the speed and altitude readout displayed on the screens on the back of the seat on DJ. Is it GPS referenced etc? Travelled from TSV recently and the readout was 12880m which converts to 42000'. Is that correct, can a B737-700 go that high or is the readout not that accurate?

[Yusef Danet]

Gets its information from its own on board GPS, under the dome. GPS-derived altitude is rarely accurate.

737NG doesn't go above 410. Except maybe on delivery flights when necessary, and even then only in the days before recorders were used to ping every out of tolerance situation.

[Going Boeing]

GPS altitude normally shows approx 2000' above the standard barometric altitude when cruising in the 30-40,000' range so I suspect that the DJ B737 was cruising at FL400. :)

[jed_thrust]

I think you'll find GPS altitude is quite acurate.

The reason it shows high in this part of the world (and lower than displayed altitide in northern parts - say around Shemya) is because it really is showing your actual height above the assumed surface of the earth, not some number derived from a standard pressure setting in some column of air that doesn't exist except in text books.
In my box the normal order of merit of the GPS is 207ft - that would be in all directions, ie a bubble.

Depending on your radar, you may be able to see some ground returns at around the 6.5nm point (normally 45 degrees from the front) (independant of the tilt). They should be your vertical side-lobes; when multiplied by 6080 should come close to your GPS altitude. I have tried this all over the world and they always match very closely.

Moving on to aircraft manufacturers height limits - my understanding is that they are mostly oxy related. So flying at 41,000 on 1013 will always give your oxy system the same perfomance notwithstanding the fact that your aircraft may actually be at 43,500 (above the sea).