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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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Old 24th Dec 2020, 10:42
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BFU has published an interim report. It is accessible (in English) onr their website and the AvHerald features a decent summary.

Extract:

QUOTE

The examination of the airplane after the landing showed that the connecting lines of the left and right static ports were not linked with the respective ADMs (Fig. 5).

The maintenance work taking place prior to the flight included opening the pneumatic lines, flushing them with dry air and closing them again. The subsequent leak test and system test were meant to ensure proper function of the pitot-static system. On the respective job cards these tasks had been signed as performed and released.

UNQUOTE

While the report gives some details on the individuals involved, it is not clear which organisation achieved this; Lufthansa or Lufthansa Technik. Hopefully the final report will go beyond that and try to identify the systemic cause involved, if any, and not stop to protect the reputation of some well established organisations, including Lufthansa, Lufthansa Technik and LBA. This is common belief in Germany that they are infallible and there is no need for proper oversight.
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Old 24th Dec 2020, 10:44
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The BFU report:

(could not include it in the previous post, as I was just short of the 10 posts threshold required to include URL)
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Old 1st Jan 2021, 04:42
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What surprises me, is the radio altitude reading being at 0 throughout the flight on the chart. Is the RA disconnected at LH until 2500ft in descent?
If ATC told them they read 200ft all along, a quick check of the RA might help. Or am I completely off on this?
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Old 1st Jan 2021, 07:27
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Radio Altimeter
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Old 1st Jan 2021, 07:54
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I know, it was more of a rhetorical question ....

"In almost all cases, the display of radio height ceases when an aircraft climbs through 2500' above ground level (agl) and recommences when it descends through 2500' agl. This is confirmed visually by the appearance/disappearance of an 'OFF' flag and emergence of a pointer from behind a mask or activation of a digital display."

.... and therefore i am still wondering about the chart RA readout ......

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Old 1st Jan 2021, 08:23
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The RA readout scale is the brown one to the right. It indicates 4000ft most of the time.
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Old 1st Jan 2021, 08:43
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Now i got it, thanks!
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Old 5th Jan 2021, 08:23
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Good job by the pilots. As always recognition is the hardest part. Looks like they got to 300kts with the flaps out! Be interesting to read the full report and see how effective the relatively new checklist was. Sounds like the standby ASI may have been reading correctly? And perhaps standby ALT as well. And radalt works below 2500ft.
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Old 11th Jan 2021, 16:01
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Is my understanding correct that is was the electrical plugs that were not inserted? What kind of transducer is this? Strain gage? Is there no self test programmed in to the box that makes sure on startup that the ADC readings are in the expected range?
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Old 11th Jan 2021, 16:06
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Not connected static pressure lines

Look here
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