airfoilmod

"The EEC responded correctly to a reduction in fuel flow to the right engine"

Read your block quote again, there was a reduction in fuel flow. To both engines, followed by correct mechanical responses. Cavitation could not have happened if Fuel had been flowing within parameters.

"Followed by a similar response in the left EEC to a diminished flow..."

Since both engines continued to run, though not at commanded thrust, one assumes ignition was present, but insufficient Fuel to produce commanded thrust. Interesting thought though, and #2 did cease spinning prior to cowl crushing at impact. Hmmm.

chase888

If core icing did occur, then the fuel most probably was no longer homogenous, particularly if wax was floating on the surface.

Most probably everything worked as advertised, but the heavier parts of the fuel(and water) did not possess enough heat(kJ) to provide the required thrust, despite the amount of fuel in all probability being correct for fuel in its normal condition.

Not sure, but I estimate that the fuel delivery pipe would be around 4" dia to give enough fuel for max. power, so ice or anything else would not restrict flow, particularly as the fuel is under pressure.

My final 2 cents worth is that evidence of cavitation on the pumps is only significant in that it takes quite some time for cavitation to become evident on the impellor surface, so most unlikely to have been a contributor to this problem.

Cheers

Green-dot

Dear Oluf,

After reading the AD, i think you are taking this passage out of context.

The statement in your post is incomplete. It is preceded by, i quote:
"This AD results from reports of engine surges and internal engine damage due to ice accumulation during extended idle thrust operation in ground fog icing conditions. We are issuing this AD to prevent internal engine damage . etc. . ."

Shutdown of both engines in this case could occur during or immediately after take-off, resulting in a forced landing. If there would be a relationship to the BA38 "grass landing" i would have expected the AD to have included prolonged CDAs in icing conditions also. Since the AD does not, i read this AD as valid in ground fog icing conditions only.

Also, there is a difference between ground idle (minimum idle) and approach idle. Approach idle is automatically selected in flight, resulting in a higher engine thrust setting when engine anti ice is on or when landing flaps are selected. For the RR Trent the EECs use EPR as primary thrust setting parameter. If core icing would have been a factor i would assume EPR would have started to deviate from normal settings in relation to the other primary engine indications, N1 and EGT. If not noticed by the crew, i think they would have noticed if this were the case, this would have certainly shown up in the DFDR and QAR parameters. No mention about such deviations is made in the AAIB reports.


Regards,
Green-dot

airfoilmod

see page 34 (this thread) post #662.

Captain Carbaugh, Boeing chief pilot, "The fuel pumps had been cavitating not long before impact, perhaps as a result of a fuel restriction or low temperature...etc." So Boeing places cavitation in a frame well within one incorporating cause. It is consistent with starvation or diminished flow of Fuel. It also places focus on Roller, not that that was anyone's intent.

Oluf Husted

Dear Green-dot,

Point taken, the AD 2008-02-05 does involve ground fog icing conditions only, and that in e x t e n d e d periods of idle power.

The BA38 probably flew a very extended period at "flight idle" power, from FL400 to 780 ft. Since engines have slightly different "lowest idle RPM" and the AD deals with "core ice" problems, I still think BA38 could have had some ice build-up, enough to make the engines "hesitate".

Furthermore this AD claims to be issued to lower the risk of both engine shutdowns, but all it does, is lowering the visibility range, where pilots should/shall do "Run-ups" from 1000meters to 300meters in freezing precipitation.

This is very strange, since the renowned Norwegian Meteorologist Åsmund Rabbe already in 1999 revealed his findings: "That ice danger goes UP by factor 100 when visibility, in freezing precipitation, increases from freezing fog to freezing rain, this due to droplet size." (if bigger, far worse)

Maybe the "timing" of this AD (six days after) was just accidental, but to start doing far less "Run-ups" has earlier resulted in engines being damaged by ice (on the ground and in the air) at Oslo Gardermoen 14. dec. 1998 (20 engines) and at Denver Airport in 2002 (15 engines)

Oluf

woodpecker

So it's just a coincidence that, while this "core icing incident" unfolded the evidence is that everything in the FADEC worked flawlessly except that the fuel flow never reached the commanded level.

I think not. Less than commanded fuel flow is a fact, core icing is not. Show how the two could be inter-related then you might have a case, but until then ......

BOAC

- can you direct me to the source of this fact as I was unaware of it? As far as I can see the AAIB state both engines were running but delivering less than adequate power up to impact - or have I missed something?

Shaka Zulu

@ Oluf Husted

Interesting site you have however you are starting to misinterpret AD's and connecting it up to BA38. You may be right (can't exclude any possibilities at this stage) but what you are saying can't be connected up with the evidence given.
Reading the report you could have seen that the engines weren't operated at Flt Idle and App Idle from F400 to 780'AAL. And for the many BA38 flights I have operated into LHR, a flight idle approach is VERY VERY unusual.

The reason for the AD from RR was because more engine data had been collected over it's running life henceforth they amended the ground procedures for core ice shedding.
One thing I would like to say though: Why does Cathay operate the EAI and WAI manually, where so many 777 operators don't?

Mariner9

Wax is (a lot) denser than kero - it will sink not float. Though what actually happens in a cold tank is that the wax layer "grows" outwards from the cold surfaces in the tank, till eventually there is sufficient wax to form an insulating barrier, greatly reducing further cooling.

tanimbar

lomapaseo you wrote:

Can you explain please or recommend a document/paper that covers this subject?

And, does the evidence indicate past icing events?

I ask purely out of interest.

Thank you, Tanimbar

Me Myself

Fellows

What if the AAIB and Boeing ended up not having a clue about what happened. Hard to come with a report when you have nothing to say. Don't you think ??
It seems to me that since there isn't anything conclusive they must be raking their brain to come out with something that isn't damaging too to Boeing, BA and finally the crew.
Still, I would think Boeing has a lot to answer for.
I am just patiently waiting for the final report. All these speculations are, in my view, a waste of time.
The only undisputable facts are :
- Both engines retarded to flight idle ( didn't stop !! )
- Crew saved the day.

Oldlae

Sunfish.

The AAIB report states that shortly after the FO took over the AT commanded an increase in thrust from both engines. The engines then responded initially, therefore fuel flow must have inceased albeit momentarily.

oxo

We've had nothing from the AAIB for some months now. Anybody know how long it might be before more information is forthcoming?

Bis47

1. Both engines retarded somewhat above flight idlle. Too bad the AAIB does not state exactly how much ...

2. The crew saved the day? Can you bring some insight? Because, according to the AAIB :
- the "flying" (co-)pilot forgot to fly the aircraft - just doing nothing, letting the autopilot fly the standard glide slope, bleeding airspeed down to the stall.
- the captain failed to monitor copilot lack of responsiveness while the speed was decaying down to stall speed at 170 ft agl. Stalling the aircraft from 170 feet led to a very hard crash landing. Other options were clearly available.
- neither the captain nor the copilot managed to restore engine thrust.

Actually we don't now exactly what were the crew actions if any. The release of the VCR will bring some insight ...

You shoud know perhaps the basic principle of crew coordination : The Flyin Pilot FLIES the aircraft, The non flying pilot "manage" the flight. Both crosscheck each other. It works pretyy nice in normal operation.

In hard emergency ... no room is left for crosschecking. That is the "two" pilots crew shortcoming.

So, perhaps the two pilots were just "frozen" ... Nobody would blame them due to the exceptionnal nature of this incident, the lack of information available to them, the lack of briefing discussion and the lack of minimum training.

However, writing that they "saved the day" is a little far fetched ...

Spaz Modic

Can't schedule fuel to the injun when there ain't any in the tanks.

stickyb

I think that is what the report says.

Quote:

At the point when the right engine began to lose thrust the data indicated that the right engine EEC responded correctly to a reduction in fuel flow to the right engine, followed by a similar
response from the left EEC when fuel flow to the left engine diminished.

The quote says specifically that there was a "reduction in fuel flow" to the rigght engine, and that the "fuel flow to the left engine diminished"

For those statements to be made something must have been measuring fuel flow, and those measurements must be in the hands of the investigators.

wilyflier

Bis47,
.......I think for whatever reason the stall did not occur at 170 ft . Free fall from that height calculates a far higher vertical speed than the 2000 ft per minute indicated by the damage.(Edit - I assumed stall to occur from an existing descent rate of about 1100 fpm)
......My rough calculations indicate a stall about half a second before impact, below 50 ft (I got a nominal17ft agl) with the nose just beginning to fall, such that there was no visible tailstrike mark.
....I guess if it was in a mushed but still steady descent at 2000fpm there would have been more tail down

Me Myself

Yeah ??? Like whot ???
I did what happened to them on the sim, very same spot and apart from the fact I disconnected the A/P right away, I just flew the aircraft to the very same spot they did, just didn't stall, or very close to the ground. At any rate the motion didn't trip meaning it wasn't too hard of a landing.
I knew what was going to happen.......they did not !! I don't know who you fly for, but I do not remember my outfit training me for the loss of 2 engines at 700 ft after a 11 hours flight........or maybe I missed class that day........again.

They bloody did.......and nothing happened.

Now let me tell you something about the F/O " lack " of reaction. 15 years ago while on approach on a south american airport, a traffic pulled out of a cloud, right on my right hand side and the only profound thing I managed to utter was " Oh **** " He missed us by 12 feet !! ( no TCAS in those days ). I was the handling pilot and thought I had reacted pretty swiftly. As it turned out, I disconnected the A/P 7 sec after the initial conflict.
The skipper only understood what happened once he saw the traffic on his side and I think we also got a " Oh **** ".
Were we under stress ??? ........" oh **** YES !! " I also remember how freaked out we were that we may have stuffed up and although facts pointed to the contrary we still doubted. It was most unpleasant ( huge understatement !! ). It also took me some time to become my confidant self again. What about now ??? I love my TCAS !! Best thing invented after the dishwasher.

I think you are being most unfair totally disregarding the " surprise " factor here.
The aircraft also bled its speed when I flew it on the sim. Apparently, according to previous posts, BA seems pretty strict about their SOP's. Where I work, I would have jumped right on the controls. No right or wrong here, just different rules which kick right in under stress. That's the way it"s supposed to be.
If BA wants to change its SOP's, they'll do it in due time if they see it fit, but flogging the crew won't bring anything to the AAIB report.

atakacs

Can we all concur that in fact there was very little they could do given the odd circumstances surrounding this event and it's timing ? As far as I am concerned I would be the last to blame them but I also wonder if it was wise to proudly stage them two days after the crash as heroes...

L337

Spaz Modic:

You are like a broken record:

Yet the AAIB report clearly says: