Vietnam 787 No gear down

[Mr A Tis]

Surprised, this has not been mentioned before.
How can a 787 get to (alleged) 650ft and not realise gear not down?
https://simpleflying.com/vietnam-air...g-787-gear-up/
Have I missed something on this story?

[Meester proach]

They would have realised by the warning systems in place ,
whether that
prompted action we don’t know

[Selfloading]

Prompted by ATC
https://www.atsb.gov.au/publications...r/ao-2019-051/

[Sailvi767]

The gear warning comes on at 800 feet AGL off the radar altimeter in the 787. Probably got the warning about the same time ATC was calling.

[gearlever]

Originally Posted by Sailvi767

The gear warning comes on at 800 feet AGL off the radar altimeter in the 787. Probably got the warning about the same time ATC was calling.

Yep, think so too.

[roundsounds]

Originally Posted by Sailvi767

The gear warning comes on at 800 feet AGL off the radar altimeter in the 787. Probably got the warning about the same time ATC was calling.

Melbourne is 400’ AMSL, FR24 data shows 650’ making it around 250’ AGL at the GA?

[DaveReidUK]

Originally Posted by roundsounds

Melbourne is 400’ AMSL, FR24 data shows 650’ making it around 250’ AGL at the GA?

That would depend on whether the "650 feet" Mode S altitude from FR24 has or hasn't been corrected for QNH.

Given that it corresponded to at a point 1.6 nm from the THR, then I suspect they weren't actually at 250' AGL.

[Capt Fathom]

FR24 displays Altitude based on Standard Pressure. If there is a large difference between that and the local QNH, you will need to apply the difference to see the real altitude.
I recall the local QNH at the time was 1027mb. That’s a 420 feet adjustment.

[fatbus]

Plus crew reaction time

[perantau]

What is the terrain like on the approach? If it slopes upwards towards the runway, then 800ft on the radio altimeter may be low in reference to the runway threshold.

[DaveReidUK]

Originally Posted by Capt Fathom

FR24 displays Altitude based on Standard Pressure. If there is a large difference between that and the local QNH, you will need to apply the difference to see the real altitude.

I recall the local QNH at the time was 1027mb. That’s a 420 feet adjustment.

Yes, that's probably correct - while there are, I believe, a very small number of FR24 feeders running software that allows them to input the QNH adjustment at source, we can almost certainly discount that here.

So that would make the altitudes at the initiation of the GA (approximately):
Mode C/Mode S: 650'
AMSL: 1050'
AAL: 625'
Rad Alt/AGL: obviously dependent on terrain (if anyone with local knowledge can help, it was 1.6 nm from the THR, roughly overhead the Keilor Stadium)

[BuzzBox]

Originally Posted by DaveReidUK

So that would make the altitudes at the initiation of the GA (approximately):
Mode C/Mode S: 650'
AMSL: 1050'
AAL: 625'
Rad Alt/AGL: obviously dependent on terrain (if anyone with local knowledge can help, it was 1.6 nm from the THR, roughly overhead the Keilor Stadium)

The elevation in that area is about 80m or 260ft, so approx. 800ft on the RADALT.

[suninmyeyes]

On the Boeing 777 you would get a config warning if you select land flap and the the gear is not down, so the warning would come at about 1500 AGL. I wonder why the logic is different on the 787.

[ScepticalOptomist]

Originally Posted by suninmyeyes

On the Boeing 777 you would get a config warning if you select land flap and the the gear is not down, so the warning would come at about 1500 AGL. I wonder why the logic is different on the 787.

787 is the same.

[BuzzBox]

Originally Posted by suninmyeyes

On the Boeing 777 you would get a config warning if you select land flap and the the gear is not down, so the warning would come at about 1500 AGL. I wonder why the logic is different on the 787.

The CONFIG GEAR warning logic is the same on the B777 and B787:

A landing gear is not down and locked and one of these occurs:

• Below 800 feet radio altitude and a thrust lever is at idle
• The flaps are in a landing position

A GPWS Mode 4A warning "TOO LOW GEAR" would occur at 500 ft RA.

[ManaAdaSystem]

I’m sure they have a gear warning when you select landing flap without gear down as well, same as the 737.
That will happen much earlier.

[Sailvi767]

Originally Posted by suninmyeyes

On the Boeing 777 you would get a config warning if you select land flap and the the gear is not down, so the warning would come at about 1500 AGL. I wonder why the logic is different on the 787.

Is the same however if you failed to lower the gear you probably did not make the final flap setting. The last backup is the Radio Altimeter alert at 800 feet.

[Centaurus]

In the old days it would be called a low drag approach. Saves fuel. Left the gear down selection a bit late, that's all..

[Diavel]

Strange

To me this whole situation seems really strange, either the plane was not configured for landing, or the bells& whistles did not work. Alternatively the twr was wrong

[hans brinker]

Originally Posted by Capt Fathom

FR24 displays Altitude based on Standard Pressure. If there is a large difference between that and the local QNH, you will need to apply the difference to see the real altitude.
I recall the local QNH at the time was 1027mb. That’s a 420 feet adjustment.

Was just looking at the Denver Airport, saw several airplanes at 0feet. Unless they dug a 5280feet hole, I am pretty sure the altitude displayed is at least some of the time based on QFE, not QNH/QFE....