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Lufthansa Cargo B772 unreliable airspeed

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Lufthansa Cargo B772 unreliable airspeed

Old 12th Oct 2020, 13:06
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Lufthansa Cargo B772 unreliable airspeed

Saw this on AV Herald (link)
[Crew was] reporting unreliable airspeed. The crew subsequenty (sic) inquired with ATC what their altitude reading were, the controller responded 200 feet. The crew reported their standby altimeter was indicating 6100 feet and according to GPS they were at 6200 feet, so they should be around that altitude.
Not a pilot. What might cause the discrepancy between the altitude that ATC was showing versus what the plane's standby altimeter and GPS were showing. Which instructions/reading should the crew follow? Don't know if they were in IMC or not.
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Old 12th Oct 2020, 14:38
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The three altimeters are using different sources I assume (not a 777 pilot).
Standby and GPS ALT was around 6.000 ft, MAYDAY declared, which means they were well above sector altitude and ATC kept the airspace clear.
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Old 12th Oct 2020, 15:06
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The ATC value is probably the value that has been encoded and sent by the transponder (secondary radar information is based on the information the aircraft sends to a ping). If the static source/s involved are giving the transponder duff info (a combination of sensor fault, icing, water ingress, FMS super brain fart, unlucky Tuesday), then ATC is not telling the crew anything useful. If the satellite signal generated altitude and standby altimeter correspond, then I‘d trust that, especially as nobody would be expecting to talk to ATC at 200ft.. or suddenly find themselves there!

The last sentence In the article about the ADS-B data saying that the aircraft did not get above 250ft for the entire flight is just a reflection of the same info that ATC was receiving and reporting, low just a reflection of the fault.

Last edited by Torquetalk; 12th Oct 2020 at 15:27.
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Old 12th Oct 2020, 15:08
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Flying at 200 ft around EDDF means your aircraft is in a subway tunnel.
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Old 12th Oct 2020, 15:44
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Occam's Razor might offer a more mundane/simple explanation than the above combination, given that the aircraft had spent the previous 6 days on the ground.
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Old 12th Oct 2020, 15:49
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Well if that is true, somebody is going to feel very silly.
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Old 12th Oct 2020, 16:09
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Not the static covers

FYI
It was not the Static-covers....
investigation is ongoing and will be published in due course....
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Old 12th Oct 2020, 19:48
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Unplugged static drains inside the cabin?
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Old 12th Oct 2020, 21:38
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777 uses flush-mount "salt shaker" static ports on the side of the fuselage to measure static pressure - there are no 'static covers' as such. Although they are sometimes taped over (and the tape left on)
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Old 12th Oct 2020, 23:33
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Boeing had thought that it had found an engineering solution to the problem of unreliable airspeed with the development of the FT-ADIRU. The original QRH entry for unreliable airspeed was just a condition statement as the "box" should have taken care of the problem. If its not an issue with the static ports then possibly it is a result of a software failure in the ADM or FT-ADIRU.
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