AAIB initial report out on BA B777 crash at LHR

[gordonroxburgh]

Great overhead image.

Some deductions from this:

Landed on all 3 gear legs and bounced

Port gear went straight up though the wing pretty much on first contact, the starboard gear failed.

On 2nd "landing" the main contact was with engines and nose gear.

The aircraft stayed on the ground this time, the engines plouging through the grass, tearing off the failed starboard gear.


Looking at this picture, it was fortunately that they did not hit the concrete with their vertical velocity, the structural damage and passenger injuries could have been far worse. The soft grass obviously absorbed a lot of kinetic engery.

[SaturnV]

Awair, the initial AAIB report was based on a preliminary readout of the FDR (and crew interviews). The AAIB report states the analysis covered the final phase of the flight. As the FDR covers approximately 700 parameters, if there had been an engine shutdown and/or loss of avionics, one can rightly presume note would be made of such in the initial AAIB report. The only anomaly cited was the non response of the engines to commands for increased thrust.

There is both video and still photography of the plane just before it reached the grass at Heathrow. The RAT is not out.

With respect to this particular incident, the AAIB is fortunate to have data from the FDR and the QAR, covering several thousand parameters. That is an extremely rich data set. It also has a largely intact aircraft, with an undamaged cockpit and quite probably undamaged avionics. If the data points to a potential hardware failure, the suspect equipment can be examined and tested.

In my opinion, the more days that pass without the issuance of an AD or SB related to this accident, the less likely that the cause will be a hardware failure or a software error, at least a failure or error that might be replicated or present in the systems of other 777's.

[OVERTALK]

UNMuddling the Thinking HERE

In response to the post by OVERTALK at #268 of this thread,

VNV2178B said:
The problem with P30 icing on R-R engines has been known and compensated for at least since the RB211 FAFC equipped units. I can see no reason why Trents are not similarly fitted.

Even if P30 is lost the FADEC will fail to reversionary mode using speed and temperature rather then EPR as the main control parameters.

I am not allowed to speculate further.

However to quote further (below) from the AD itself, it would appear that the FAA had genuine concerns about the possibility of LOTC (Loss of Thrust Control) on the Triple 7 - which is exactly what happened to Flight BA038 after an extended period of cruise in very cold temperatures at height - during a 12 hour trans-polar operation. In addition, any prolonged CDA descent at near idle power has the potential to:
a. Allow greater than normal cooling within the nacelles

b. Disguise the fact that the engines are "locked at/near idle" due to the FADEC's reference pressure sensing lines becoming obstructed by waxy ice crystals.

I'm not aware whether or not the FADECS are just similar (or the same) on GE, Trents and P&W, however the possibility remains that the problem is replicable across the GE's and Trents. I doubt that it is just a mere coincidence.

QUOTE FROM the Airworthiness Directive: (link at http://tinyurl.com/2nx3ym)

Simultaneous LOTC Events

The FAA is especially concerned about the possibility of simultaneous LOTC events on both engines installed on the Boeing 777 series aircraft due to common mode threats, such as certain atmospheric conditions that may result in ice in the Ps3 or P3B pressure sensing system and causing corrupted signals to the FADEC in both engines.

SUMMARY: This amendment adopts a new airworthiness directive (AD) that is applicable to certain General Electric Company GE90 series turbofan engines. This action requires visually inspecting Ps3 and P3B sense lines and full authority digital engine control (FADEC) Ps3 and P3B sensing ports and fittings, cleaning Ps3 and P3B fittings and sensing ports, purging the Ps3 and P3B systems of moisture, and, if necessary, blending of high metal, nicks, burrs, or scratches on Ps3 and P3B fitting threads. This amendment is prompted by seven reports of loss of thrust control due to corruption of the signals to the FADEC caused by water freezing in the Ps3 sensing system. The actions specified in this AD are intended to prevent loss of thrust control due to corruption of the Ps3 and P3B signals to the FADEC which if it occurs in a critical phase of flight, could result in loss of aircraft control.

Interim Action

Both Ps3 and P3B pressure systems incorporate weep holes that allows drainage of water in the lines that may accumulate from condensation or ingested water; however, the field events and the investigation have determined that these design features may not always be effective in eliminating water from these systems. GE is assessing design changes that will prevent water from freezing in these systems and causing corruption of the signals to the FADEC. The requirements of this AD may change based on the ongoing investigation of the root cause and field inspection results, and future rule-making may be necessary.

[ACMS]

OVERTALK: I understand that BA38 held at LAM? If so they WOULD have spooled up power more than once and your theory above might not hold water.

[Ian W]

:
Therefore I do not see that CDA per-se would have any bearing on this although it is possible that the BA or NATS procedures for flying them at LHR might have some impact.

That wasn't the point I was making. It was that a continuous descent at idle (if that is what occurred in this case) might have masked the problem whereas a step down to a platform altitude would have required a power-up and so revealed the problem at an earlier point in the approach. The crew would then have had the option of delaying gear/flap which might have enabled the aircraft to reach the runway.

I fully agree with your point.
If you read my original post I said that CDAs were poorly defined, and that the flavour of CDAs used by LHR were a long final approach intercepting the glide path several thousand feet earlier than normal. I also stated that NATS and BA had agreed procedures that were particular to the approach at LHR.

In this case the procedure was the 160 to 4 as it appears to be known. This does not seem to have been assessed for the risk of a double engine failure to spool up after the slow down from 4 to ~2 miles. In fairness this has not happened before on this approach. However, in safety research a risk greater than '10 to the minus 9' is (supposedly) unacceptable - and that would mean (roughly) something that happens once a second cannot go wrong more than once in 32 years. The acceptance rate of LHR is only around once every 40 seconds at best and the procedure has only been in place around 2 - 3 years (?). So although it is a rare event it may still unacceptable in 'pure' safety terms - but then practice and theory are often different. (Before the anal mathematicians start probability theory on me - I know that probability does not mean it can't happen immediately but that is not the point - it was not considered)

So after all that - NATS and BA may well change the procedures a little - I read in an earlier post that some operators prefer to be stabilized on the approach a lot earlier - I think that this is justified. There comes a time when you have to balance noise nuisance with safety.

However, I do not think that CDAs will go away as the potential financial savings are huge. Research I did for Atlanta showed that savings of 45 flying hours per day were possible. Added to the research from SAS with savings of up to 1000Kg of fuel per approach and the argument for a full CDA is difficult to refute. But late spooling up of engines may be seen as too much risk - and this may result in stabilized approaches from say 5 miles.

This is where safety meets environmental impact (read political problems) - and who knows which way the decision will go?

[mocoman]

NATS and BA may well change the procedures a little

c.f
suggestions made recently regarding the modification of the EGLL ILS to instruct inbounds to land further down the runway for noise/environmental reasons.

These proposals would have made the incident far more serious; landing on hard standing rather than soft turf would have exacerbated the problems already present within the aircrafts' final approach profile as well as exposing the passenger terminal, and aircraft taxiing, areas to more direct exposure to the incident.

Additions:
I gather that BAW038 held for one circuit at LAM.
Added 'EGLL'

[pasoundman]

Oldlae
My concern is that whatever caused this incident may not have been recorded in the FDR because the relevant parameters have not been included

There was also a quick access recorder on this a/c. It will have been recording more data than the DFDR does.

[kuningan]

Great overhead image Some deductions from this:

It also appears that the disturbance of the ground differs between the right and left engine tracks - that could be because of different soil subsurface - or it could be because of differing power outputs - the Mail photograph suggests a lot of sandy soil being blown up on the lhs - reverse thrust?

[Dak Man]

Is it conceivable that the RH engine had already shut down and the approach was continued and subsequently the LH engine shuts down at 600' AGL and is still windmilling at impact.

The pictures of the turbo machinery seem to indicate such a scenario, i.e little or no fan damge to the RH engine and a contained fan blade separation of the LH engine.

So, the "failure" of both engine control systems may not have been a simultaneous event as previously speculated. Does this, once more, indicate a fuel starvation / contamination issue.

[OscarLimaIndia]

QAR's record less data, that's why they are QAR's

[Profit Max]

Originally Posted by OscarLimaIndia

QAR's record less data, that's why they are QAR's

Suggested reading (good description of a QAR):
http://www.tsb.gc.ca/en/reports/air/...rep1_11_05.asp

[VnV2178B]

Overtalk,

I won't deny the possibility of a P30 problem, at this stage anything could be true, just wanted to point out that it is known and there is a mitigation strategy for it. Maybe the strategy doesn't work...

VnV

[Hand Solo]

Originally Posted by OscarLimaIndia

QAR's record less data, that's why they are QAR's

Errrrr, no. QARs record much more data. They are QARs because they are not crash protected so you can get to the data Q.

[NSEU]

QAR's may have access to more data, but does that mean they necessarily record more data onto the PC card?

I thought the idea behind QAR's is that they could record bursts of selected information at selected points throughout the flight. i.e. stuff that maintenance/ops needed to know.

Of course, they can also be programmed to record additional data by unusual events (but will this be brief snapshots... or more useful continuous data?).

Does the QAR, DFDR and CVR run on the same elec (power) busses as the nose landing lights If so, we might get some pretty good info from one of these boxes .... Although, having said that, the AIM's system might not have been operating at 100% (considering the report that cockpit displays failed).

[r011ingthunder]

@NSEU who said, "Does the QAR, DFDR and CVR run on the same elec (power) busses as the nose landing lights"

I don't know, but I would assume that these devices would run on battery in the event of power outtages, after all what use would they be otherwise in recording data if the power went down?

[CargoOne]

I don't know what data is recorded on 777 QAR, but on our a bit older aircraft type where QAR was installed only through post-production SBs, QAR is basically recording 100% same data what is recorded on FDR. In fact both FDR and QAR are connected in parallel to the same data supply bus.
May be on a newer types where QAR is a standard equipment installed on production line, there are more options on what data you can record.

[SaturnV]

From a post by P2 earlier in this thread:

The QAR (for SESMA/FDM/FOQA work) will record as many parameters as the installed data frame is designed for, (QAR software) and at sample rates that the frame is similarly designed for. The DFDR is capable of this as well but typically DFDR data frames are smaller and at less frequent sample rates for many parameters. Sample rates of 16 frames per second are possible but are expensive in terms of storage and recording capability. Sample rates from once every fourth second to eight times per second are common in both DFDR and QAR dataframes.

All this is by way of clarifying that "700 parameters" and "2000 parameters" is not a fixed, determined number. Our own 777 QARS are taking in more than 2600 parameters

(Bolding mine)

[hetfield]

17:1, which is about the same as the L/D of a modern airliner.

But not with gear and flaps extended.

[NSEU]

I don't know, but I would assume that these devices would run on battery in the event of power outtages, after all what use would they be otherwise in recording data if the power went down?

Never assume.. I haven't got the relevant data with me for the 777, but all the other Boeings have these devices on the main elec busses. I can only imagine that this is because the designers think the pilots need the backup electric power more than the recorders. A competely flat battery will increase your risk of crashing considerably.

Would a windmilling fan be able to generate electrical power?

Not at approach speeds. A 747-400 pilot tells me that during cruise, a dead engine remained windmilling fast enough to provide proper power. "N2" or "N3" engine rotor speed (depending on the engine), has to be over 50% or so for the generators to produce power of a quality which will be accepted by the airplane.

Rgds.
NSEU

(Edit) According to the Maintenance Manual D&O, 115Vac power comes from the Right AC Xfr Bus, DC control power comes from the 28Vdc Main Bus. The Left Nose Landing Light uses the Left Xfr Bus and the Left 28VAC Main Bus... but no data as yet for the Right Nose Landing Gear light... but I'm guessing it uses the opposite busses... so the FDR will probably be getting good power.... but.. we should never assume

[r011ingthunder]

@NSEU
I stand corrected then
Although there is no harm in assuming once you admit that's what you're doing!