Comments on: Boeing 777 accident: Engineers giveth and Programmers taketh away

By: Bill Rendell

Bill Rendell — Fri, 31 Oct 2008 10:44:41 +0000

The AAIB report is very detailed as expected. However, it does include more than a few estimations and presumptions. I would have expected such a report would be confined to established facts. However it is interesting reading that provokes thought by all interested parties.

I dont believe much attention was paid to the probability of a reduction in engine oil temperatures after a lengthy ’staight in’ descent. Thus reducing fuel heating efficiency. In turn, adversely affecting dispersion of ice into EDP’s.

Should that be a possibility, then certainly, oil/fuel heat exchangers ‘do’ require modification to include an alternative means of maintaining efficiency under those conditions.

To Peter Field// The lube oil may not be that hot; using supercooled fuel to remove heat from it, after a legthy period at flight idle.

Let’s trust it will be sorted soon.. A similar accident surely would not meet the same fortunate conclusion///

By: peter field

peter field — Mon, 08 Sep 2008 16:07:47 +0000

Having seen the new, very detailed AAIB report, ice may well be a contributory cause. But now having seen the layout of the kerosene fuel system, a thousand times more risky is the spill return from the fuel metering valves passing back into the inlet of the h.p pumps AND the fuel preheater just upstream. Any problems with the control of the preheater, receiving very hot lub oil from the engine, and the kerosene could easily get up to gassing temperature… a situation exascerbated by the spill back control. The very constant fuel flows of 5000 and 6000 lb/hr in the last 40 seconds, could be caused by the pumps handing an amalgam of gases and kerosene. This is the elephant in the room. The Report cleverly does not mention fuel temperature AFTER the preheater, how the preheater is controlled; or how the flow meters work. The actual liquid kerosene flows could have been a lot lower than the above figures.

By: J Gittins

J Gittins — Sat, 06 Sep 2008 10:44:47 +0000

Sirs, the report on the 777 accident is now published, to quote a lady in a letter to a newspaper eloquently commenting on a 2 year study by a university in Belgium ” After 2 years hard study they have come out with the bleeding obvious”
As time went by after the occurrence we heard many theories given by both manufacturers and pundits, strangely enough the airline was staying very quiet, this led to people ‘experienced aviation people being very suspicious’
HP pump cavitation, both at the same time, hardly!
Some sort of fuel contamination? FM procedure is for straight feed on approach each engine dependent on its own tank.
Fuel shortage? with FMS you would have to work at running out of fuel ‘Fuel on Board, Distance to Go, Fuel remaining at Destination, all on permanent display two separate CDU’s.
There was only one common denominator “ICE” the general need for Engine ant-ice ‘ below +5c with visible moisture, “those conditions did’nt prevail”
Cold soak! in a later report the CAA stated that the A/C had encountered an area of very cold air -74 deg C over Siberia/Scandinavia the aircraft I believe was using fuel with a freeze point of -47 deg C.
An extract from the fuel management section of the B747 FM states that fuel tank temp should not be allowed to decrease to within 5 deg’s of min fuel freeze point. If total outside air temp approaches -65 deg’s then tank temp should be monitered as indicated temp is TOAT minus 25, action to be taken is to shake the wings and if this is not successful descend to a lower altitude.
Flying many times between Alaska and London we would get a TOAT of approaching -65c and the fuel temp would be hovering around -35, but then the F Eng had a gauge that could be monitored (two things missing on the triple 7) I find it hard to believe that with a prolonged temp of -74 the tank fuel did not fall below -34. Also as the vol/mass of fuel in the tank decreases conduction of hot to cold increases and in descent with idle power there is little fuel movement. As for the FADEC I think in 2000/1 there was a special check initiated on the American engine this entailed checking the joints of the pipes supplying air data to the FADEC to eliminate moisture that had frozen and caused nil response to thrust demand.
Well the report is published but I fear it is a compromise as ever between the aviation authorities, manufacturers and airlines. The push towards full automation, need to know training, min cost, min crew, min fuel, min engines and min diversion distances.

By: David

David — Tue, 29 Jul 2008 10:34:42 +0000

I do not want to even take a chance on guessing as to when the B-777 investigation will be complete. Now, with the stakes being so high .That is, the Boeing Vs Air Bus competition for sales being what they are at the moment. However, had the BA B-777 accident occured in France instead, the JAA investigation would by now be history.
The British have this unwritten attitude and behaviour towards the Americans. Go anywhere and we will blindly follow you. Yeah, be it to Iraq , Iran or Timbuktu. Worry not how you blunder , we’re there to muffle the thunder.
The truth will however come out in the open. It always does.

By: Flt.Eng.(retired)

Flt.Eng.(retired) — Fri, 25 Jul 2008 10:04:42 +0000

Where can fuel turn to slush, not freeze, and reduce the flow to the engine after a long cold soak at altitude ?
Filters?
Fuel cooled oil coolers ?

By: Toss

Toss — Sun, 20 Jul 2008 05:10:24 +0000

Its taking a very long time for a complete report to come out.

By: Bill Rendell

Bill Rendell — Thu, 29 May 2008 10:09:22 +0000

http://www.aaib.gov.uk/cms_resources/S3-2008%20G-YMMM.pdf

For those who have not yet seen it. Above, is the reference for the latest aaib report.

Perhaps (if it is not aready underway) it would be prudent to investigate possible restriction of the tank vent system and its effect upon’a less than ambient’ pressure head above the fuel, on descent.

By: Bill Rendell

Bill Rendell — Thu, 10 Apr 2008 12:03:50 +0000

Peter, Thanks for your plausible and detailed explanation of my query about older slimmer power plants// I found it interesting and could identify with your line of reasoning.
PAPIS or ‘line ahead’ approaches may easily cause the ‘big boys’ to dump thrust or eject exhaust gass, in precisely the same area. Combined with 50% reduction of power against 25% on thinner 4 motor jets; as well as the added penalty of increased spool up times, could well reduce the margins we have been used to. (add to this the fuel icing probability in this case)
Living in a quieter area close to Heathrow, I have also observed the apparent reduction in the ‘line ahead’ distance between approaches. The ’supply and demand’ effect upon traffic density can surely only reduce the expected safety margines// unless modern technology is capable of (at least) keeping abreast. But at what cost??

I am sure an alternating !curved! approach path would help to reduce the compressor contamination theory, but of course in turn, would cause concern for residents living below the 3 flight paths’, as well as commercial considerations of costs (and who will pay ???)

After very many years in aviation, I know, that maintaining ‘even minimal’ safety and quality standards do not come cheap. However, Jo Public will most likely try to fly with an ailine charging less than the pioneers. (Band Wagons??)

There is yet another lesson to be learned from this accident. Let us hope it will be learned and that “All” will take note//

By: egl

egl — Tue, 08 Apr 2008 19:14:07 +0000

April 7 WSJ article on engine icing:

“The odds of both of a plane’s engines shutting down at once were supposed to be about one in a billion. Since 2002, however, internal ice has been blamed for at least 14 instances of dual-engine shutdowns, called “flameouts,” and several times that many single-engine outages. Investigators now believe that since the mid-1990s, so-called crystalline icing has prompted dramatic power drops or midair engine stoppages in more than 100 jets. So far, the flameouts haven’t been blamed for any crashes, because the engines on big commercial jets have always managed to restart.”

By: peter field

peter field — Sat, 05 Apr 2008 11:51:26 +0000

Bill, you were right to challenge my over simplistic last sentence that older thin turbo-jets would be unaffected by unsatisfactory inlet conditions. I meant that in days past, bad inlet conditions would be less likely to compromise thrust so severely. There are several reasons.
Older “heavies” tended to have 4 engines, thus reducing risk of all exactly in line to scoop up bad conditions; the long sleek engines had a far smaller inlet cross sectional area so less lileky to scoop up vast volumes of bad air; the sleek engines had a far smaller radius of gyration so could spool up quicker to compensate for compromised conditions; the older engines got the same “oomph” (mass of air times velocity rise) by more velocity and less mass flow, so less affected by compromised mass flow; the giant 110″ fans of the 777 do most of the thrust and are very affected by vortices/temperature. My gut feeling is larger numbers of smaller diameter compressors are less prone to trouble. Compromised conditions on older engines could temporarily give poor performance but didn’t have the extra complication of fadecs scratching their heads working out best adjustments which can take valuable seconds; older planes may not have all followed such an accurate flight path where all planes add thrust (and dump extra exhaust gases)at exactly the same place; large fan jets need extra fuel (and exhaust gases) to accelerate the 110″ fans first before extra thrust is obtained.
But you are right; most likely cause is a fuel problem per se or a mixture of fuel problem and fadec confusion.
Its just that when one sees (from the M25 at night) convoys of jets one after the other,coming in to land, millions of times globally in a year, one wonders that a chance in ten million of gathering hot vitiated gases lingering, could just cause a mysterious mishap such as this.