Qatar. Take-off FUBARed. Again.
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Running the numbers...
Some of the headlines suggest the aircraft came to a stop from a speed in excess of 100mph. I also saw from the video that the aircraft came to a stop basically at the displaced threshold. This got me wondering: What is a typical accelerate-stop distance for a widebody passenger jet? How does an A350 go for 30 seconds and end up at the *beginning* of a runway??
As it turns out, JFK's 22R has a 3425' displaced threshold. From the video, I counted about 32 seconds from first motion to stop, split about equally between acceleration and deceleration. Assuming textbook physics using those numbers gives an acceleration of 13.3 ft/s^2 (0.4g, which looks reasonable for a jet) and max speed of 125kts. If the actual max speed achieved was only 88kts (ref: https://twitter.com/AirlineFlyer/sta...54919339499521), that allows for some slop and lower acceleration numbers given the apparent runway used.
FWIW, my accelerate-stop distance is 2000'. And my home airport runway is *shorter* than the displaced threshold at JFK's 22R!
As it turns out, JFK's 22R has a 3425' displaced threshold. From the video, I counted about 32 seconds from first motion to stop, split about equally between acceleration and deceleration. Assuming textbook physics using those numbers gives an acceleration of 13.3 ft/s^2 (0.4g, which looks reasonable for a jet) and max speed of 125kts. If the actual max speed achieved was only 88kts (ref: https://twitter.com/AirlineFlyer/sta...54919339499521), that allows for some slop and lower acceleration numbers given the apparent runway used.
FWIW, my accelerate-stop distance is 2000'. And my home airport runway is *shorter* than the displaced threshold at JFK's 22R!
Could it be this new ROPS technology?
As the video in your link states: "ROPS assists the flight crew during the final approach and roll-out". It's not operational during a takeoff, though the A350 FMS features a broadly similar Takeoff Surveillance function, which does what the name says in the tin.
For the avoidance of doubt and misinformation...
The A350 has no automatic rejected take-off mode, and nor does any other aircraft that I know of. In common with other comparable types, the auto brake is normally armed for take-off and then operates IF the pilot rejects the take-off.
The ROPS function is operational only during landing. If a potential runway overrun is detected (one of the top few aviation hazards in recent years) then max auto brake will be applied if auto brake is already selected by the pilot. If auto brake has not been selected, then the system will issue warnings only.
There's some ill-informed 'automation hysteria' on this thread...
The A350 has no automatic rejected take-off mode, and nor does any other aircraft that I know of. In common with other comparable types, the auto brake is normally armed for take-off and then operates IF the pilot rejects the take-off.
The ROPS function is operational only during landing. If a potential runway overrun is detected (one of the top few aviation hazards in recent years) then max auto brake will be applied if auto brake is already selected by the pilot. If auto brake has not been selected, then the system will issue warnings only.
There's some ill-informed 'automation hysteria' on this thread...
Last edited by ExV238; 15th Dec 2015 at 20:45.
I am not familiar with A350 specific system but this is from RAAS manual:
4.3.7 Distance Remaining – Rejected Take-Off Advisory
RAAS provides distance remaining advisories to provide the flight crew with position awareness during a Rejected Take-Off (RTO), refer to Figure 4-12.
4.3.7.1 Annunciation Criteria
The advisory is generated if:
Aircraft is on a runway, and
Ground speed is greater than 40 knots, and
Aircraft ground speed during the take-off roll decreases by 7 knots from its maximum, and
Aircraft is on the last half of the runway (default) or a specified distance from the runway end.
RAAS will provide distance remaining advisories as detailed in section 4.2.4. When the ground speed decreases below 40 knots, these advisories will terminate.
4.3.7 Distance Remaining – Rejected Take-Off Advisory
RAAS provides distance remaining advisories to provide the flight crew with position awareness during a Rejected Take-Off (RTO), refer to Figure 4-12.
4.3.7.1 Annunciation Criteria
The advisory is generated if:
Aircraft is on a runway, and
Ground speed is greater than 40 knots, and
Aircraft ground speed during the take-off roll decreases by 7 knots from its maximum, and
Aircraft is on the last half of the runway (default) or a specified distance from the runway end.
RAAS will provide distance remaining advisories as detailed in section 4.2.4. When the ground speed decreases below 40 knots, these advisories will terminate.
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Excluding the technical and operational aspects of this event, asking/ordering journalists to stop using cameras, whether allowed or not is a pointless thing to do. The first job of cabin crew is to ensure the safety of the passengers. Their time might have been better spent thinking about how to execute an evacuation. And let's remember, the culture of a company is expressed in the actions of its employees. The world in which we now live is recorded in detail. Nothing we say or do will stop that and it is naive in the extreme to think otherwise. Therefore, to avoid harsh judgement by social media, make sure you have a practical and common sense approach to dealing with the inevitable problems we face doing our job. A good start might be to stop your senior executives saying that serious events like over-runs are a common event. So unless we can uninvent things, let's learn how to deal with the world as it is.
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Quote,
"The TORA did not take into account the extra distance of the displaced threshold."
If that was the case, I'm curious as to why this didn't show up during the take-off performance calculations since they would use the same database.
"The TORA did not take into account the extra distance of the displaced threshold."
If that was the case, I'm curious as to why this didn't show up during the take-off performance calculations since they would use the same database.
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The root cause of the event was a CODING ERROR in the Jeppesen Airport Map Database.
This was a Jeppesen error.
The TORA did not take into account the extra distance of the displaced threshold.
This was a Jeppesen error.
The TORA did not take into account the extra distance of the displaced threshold.
Now that there is an ac that tracks runways length, I am certain that many, many more errors in these databases will be uncovered. Similar to RNP, the navdatabase information wasn't really used, and errors went unnoticed. I have seen may runway lengths that are complete bull****.
I found it really irritating that the runway endpoint in the database, according to FAA standards, is not measured at the threshold, but at the physical end of the runway pavement, leading to many errors in navigation when looking at TCH and the waypoint. (just like the displaced TCH at PSP, which are significant. Look at the NOTAMS, still do not reflect the DT)
The ac now have the ability, with the new systems to track and automate many functions. This will cause many problems in the short term, just as with the data for RNP, as the data has never been used, checked, nor vetted.
It will be necessary for many agencies to get off whatever they have been riding and do their jobs...
Back to the issue...
I guess my question would be, why does the error show up after roll, not prior to?
why does the error show up after roll, not prior to?
I'm guessing the designers don't want the system triggering a nuisance warning every time the aircraft is on a "short runway" that's being used deliberately, at low speed, perhaps as part of a taxi route.
FWIW some of the caution/warning features on the RAAS on our Boeing are inhibited until you reach 40kts ground speed for exactly that reason.
Last edited by wiggy; 18th Dec 2015 at 09:40.
