bearfoil

Landroger

I discard "holes in cheese", and Occam is more like a group vote than a tedious research into cause and effect. If I could call up the spirit of Pinkman I would welcome his input relative to water/fuel/ice.

I think you envision a puddle of Water freezing at the bottom of a tank or an elbow in the transit pipe. There is always water in fuel, that is a given. In the least amount perhaps 7ppm. Depending on piping architecture, tank pressure and boost pumps, the system is engineered to preclude clogs of solid water Ice getting to the engines. From the beginning here, from Boeings chief safety pilot to posters on this thread, a theory of migratory slurry came about that was theorised to have broken off the walls of piping to flow with the current to end up at the FOHE face, where it plugged fuel flow after several seconds of full chat, a matter of collected data on the record. GE versus Pratt, Chinese versus US or Brit fuel, bowser this, sumping that, or not, and the procuring cause of the problem was?????? UNKNOWN. The theory was not duplicable, and the mandated fix involves a little closer shave to the face for the fuel tubes in the HE cannister. Evidently, Boeing and FAA are confident the fix will prevent further occurrence of quiet Trent syndrome. Since nothing in the report explains how this happens, one may ask really?

bear

infrequentflyer789

You aren't the only one.

That shouldn't be a surprise, it wasn't to me. Since the early interim reports it's been made clear that there was some sort of obstruction in the fuel system, that disappeared before investigation. Ice / wax / slush typically doesn't stick around to be investigated, and can form and behave "randomly" making reproducible experiments practically impossible.

Realistically, "probably" was always as close as we were going to get.

What you may have missed is that the suspect is not water ice, in fact I think the AAIB may have confused many by referring to it throughout as "ice". It is actually a slush made up of fuel and water, at above the waxing point of the fuel but below the freezing point of water. It isn't clear that this is a previously known phenomenon - it isn't a well researched state of fuel, if it was known about at all.

The reported tests showed both that a spoonful of water could create enough of this "ice" to block the FOHE, and that larger quantities of this "ice" (more than enough) could acrete on pipework over time at low fuel flow rates.

AAIB: "Data mining showed that the accident flight was unique amongst 175,000 flights..."

That was a big data excercise, and found no other comparable flights, so we have no idea how many flights you would need before you would be likely to see a repeat of these circumstances. Quite possibly more than the total 777 flights to date.

To apply Occams Razor, you need to have other hypotheses that also fit the evidence. I see none. Up to now I would have said that the spar-valves were still a suspect on the info we had, but I believe I see in this report the evidence on which the AAIB have ruled that out (not as clearly presented as I would like, but I think it is there).

What I do see in this report, in much more detail than we had before, is lots of elimination of other hypotheses before ending up with the "ice" as (only) probable cause, ie. "When you have eliminated the impossible...". That isn't Occams Razor - in fact it is more the reverse of it.

infrequentflyer789

Agreed and worth noting that some 18 months ago the AAIB recommended that the regulatory authorities consider, as phil gollin says: "undertaking such research and then applying it to ALL airframe and engine combinations."

That ball has been in the regulators court for 18 months now, and it is out of order to blame the AAIB if the regulators haven't done anything with it.

Willie Everlearn

The CBC here in Canada are reporting that the crew of this flight have been off duty since the accident and the Captain "is looking for work".

Do I conclude from this that;

A. BA severed the crew
B. The Canadian media are just as good at reporting aviation stories as everyone else
C. This crew have decided to "moonlight" as industry saviours
D. Fiction is stranger than fact

Willie

Me Myself

Don't know about the F/O's, but the captain resigned last August 2009 and if he is looking for work, then we'd all be doing a good deed in closing that thread that is in no way helpfull.

Blythy

Aside from the ice stuff; there's some interesting theoretical questions that come as a result of this:

-does a three degree glideslope have enough of a safety margin for an approach vector. Would a higher slope with a lower throttle setting (hence less difference should thrust fail) be safer with regard to a loss of power on finals, or is the requirement for a better go around response more pressing (presumeably, it's faster to go around with a lower glideslope)

-Are runway safety margins big enough; should there be some sort of retardation surface at the end of runways in the event of such an incident or is grass good enough? What if it had been frozen?

-How the hell did a guy make it back on board to retrieve stuff? I know the slide at the rear right door was almost horizontal from pics I remember seeing but when did he get a chance?

-Good boeing quality control I see; with plastic ice scrapers being found in the tank; and FOD having a possible effect on the water scavenging in the tanks.

Burger Thing

Yes, of course... But the aerodynamic principles are the same. The concern is to get rid of the parasite drag. On a heavy jet with the landing gear down and full landing flaps and no thrust you decent like a stone at VREF Or you bleed off your speed down to the speed shaker in no time if you maintain a 3 deg G/S, like the crew of the TA B738 in Amsterdam experienced with their throttles closed at idle.

The difference in stall speed and hence available lift is not much at the later stages of the flap settings - but the difference in drag is enormous. Which is handy to have, if you got your engines running. It will require a rather high power setting, which gives you a much faster throttle response.

So IMHO even if they couldn't maintain the speed and raised the AoA to get more lift and therefor increased induced drag, they drag was still less then the parasite drag you have with full flaps. I think the report also mentioned, that if they had maintained the configuration, they would have touched down a bit earlier. Which seems to support my thoughts above.

S.F.L.Y

This isn't correct, as you can see on the following illustration (B787), the later stages of flaps are having a lower impact on the L/D performances than the earlier. This means lift benefits are more predominant over drag in this stages than in the earlier.



While L/D improvements resulting from flap retraction are visible on this illustration, you have to keep in mind that this is valid provided that the aircraft flies the appropriate Vref. In other words, compare the little L/D improvements that you obtain through flap retraction with the major L/D reduction caused by flying at the minimum speed and you will find out what was the most efficient way to control gliding performances. The lack of speed control caused greater performance deterioration than the flaps retraction could improve.

It's exactly like trying to clear an obstacle during a climb by retracting the landing gear while the aircraft's speed is far from Vx. It only reduces the "negative" effects.

Mr Optimistic

I admit this isn't my line of work but doesn't a given configuration give a given L/D ratio which defines the best flight path angle (best in terms of range) and the crew have to find an angle of attack which achieves the flight path angle with the speed following from there ?

S.F.L.Y

For each config you have an optimum L/D angle of attack. Deviating from this value will reduce the L/D ratio.

BarbiesBoyfriend

I agree that on a 3 degree slope an a/c is always going to be short of energy if it has a complete power loss.

So why not fly a bit faster?

What, for pitys sake, is the point of flying at Vref+5, 5 miles (or more) out?

Is it SO hard to slow down when near to the runway?

The extra 'handling speed' is useful too.

L337

Because a stable approach is a fundamental tenant of a safe operation of a large commercial airliner. Accurate speed control is absolutely vital to putting the aeroplane down in the right spot and getting it safely stopped.

It is? Why? Are you suggesting Boeing Airbus et al need extra speed to handle better? Whatever better is...

Why are you posting on a subject and thread you clearly have absolutely no knowledge of?

BarbiesBoyfriend

L337

I have 10000 hours in commercial ops.

Where I work you have to be stable by 500' but they teach people to fly Ref+5 for miles before that.


Do you know what 'handling speed' is? It's not type specific.

As for flying a bit faster: I think most folk could and still be stable at 500'

Maybe you'd struggle on your type? I know not. Depends on the type. And the pilot.

L337

I cannot believe for one second that you have ever flown a heavy jet. And whilst we are willy waving. I am a 747-400 Captain, I have well over 20,000 hours of which 7000 are on 747s.

I sure would struggle to be safe if I flew as you suggest.

BarbiesBoyfriend

Well, there you go then. Don't carry any extra speed. I'd hate you to have an accident!

An extra 5-10 kts would likely have got the 038 on to the runway, is all.

My point is simply that Ref+5 is great at 500' -and you need to make it so, because nowadays you're not trusted to slow down any later.

But why at 4 miles? I mean -are you going to land out there?

(Biggest I've flown is MTOW 48000kg. Small to a Jumbo.)

Just a wee edit to add that we can be at Vref+19 at 500' and still be officially 'stable'.

captplaystation

L337 , well, I have to say you are very fortunate to always fly to destinations where there is no, or very lax ,speed control.
At LHR/LGW/STN and many many major European airports the requirement is 160 to 4.(indeed there are some that ask 180 to 4 which is exaggerating just a little)
So, if you are able 25kts to be bled off, in the case of this 777 , in the last 4mls.
Well, in my mere 16500hrs I seem to have observed most of my colleagues remaining safe whilst complying with that, what are you missing ?

Pinkman

Mariner9

I happen to be looking at a S Korean Jet A-1 CofQ as we speak. FP quoted is -51C. This particular one had bacterial contamination as it happens but that's nowt to do (it seems) with BA038.

Come to think of it, one of my colleagues dealt with a major particulate contamination (again, nowt to do it seems with BA038) on an Ulsan jet cargo late last year, I'll check on quoted FP when he returns to the UK next week.

L337

I never for one moment suggested that I do or would ignore speed controls. I said: "a stable approach is a fundamental tenant of a safe operation of a large commercial airliner. Accurate speed control is absolutely vital to putting the aeroplane down in the right spot and getting it safely stopped."

The bulk of aircraft accidents happen in the landing phase. The major cause of landing accidents can be traced back to rushed approaches, and unstable approaches. 4 miles is 1200'. With planning it is possible to be stable at 1000, and definitely stable at 500'.

Carrying unnecessary excess speed is one cause of a unstable approach.

Recent studies show that, most CFIT accidents occur within 8nms of the airfield, and a very large proportion of these are on the centreline within 3nms.

1000' is about the last point to have energy management issues resolved in order to ensure maximum capacity for the last 3nms of the approach to monitor and manage the most exposed part of the flight.

maynardGkeynes

Can anyone explain why the incident happened when it did, just before the runway? Why did it not happen earlier in the flight? To me, this is just too much of a bit of luck to have been pure happenstance. It suggests human error, possibly pilot error. But what?