Thrust Control on Finals and Wing Strength
 

The quality of this topic is very impressive - particularly from the engineers. Thank you. Here are a few insights.

Thrust Control on Finals

Thrust Control - Good guessing but lots of noise here ...

Eng 3 in ALTN Mode (N1 with -4% thrust protection) (Due EEC having insufficient valid signals to calculate TPR)

1+4 EEC errors logged. Degraded mode is purely due to loss of sensor inputs/EEC errors. Think of it as the engine in Direct Law (no thrust protections!) (Due EEC not able to calc TPR demand. So N1 commanded as a function of TRA and altitude)

One engine in a degraded mode does not cause another symmetrical engine into degrade mode. Airbus never matches thrust - it's against their philosophy "manual thrust is manual thrust!" - not like pseudo Boeing "manual thrust".

So 1 & 4 in Degraded (think Direct Law) Mode (no protections)
3 in ALTN mode (think Alternate Law with protections)
2 was in Degraded mode (not surprising given there were so few sensors left)

NO engines were in a normal mode.

This is why 1,2,4 had N1 centric displays (Degraded) and 3 had an TPR centric display (ALTN) (though thrust set via N1 with 4% pad).

Thrust control on 1,3,4 all 100% correct (but differing protections)

Auto Thrust inop due to MORE THAN 2 eng in Degraded Mode

1+4 thrust levers held constant to: (not in any manuals)

1. permit very accurate (vernier) total thrust -> speed control on finals
2. minimise thrust missmatch->yaw->roll->flight control demand on finals with thrust changes (ESSENTIAL when little excess roll control available)

1+4 WAS NOT held at constant thrust due to them being in Degraded Mode (illogical).

Conclusion: The three level 380s thrust system has incredible fail operational capability.

WING STRENGTH

1. Not a problem. Wing loaded ~23% to ultimate limit (1.1/2.5 X 440/569 X 1/1.5) (Max 20 deg AOB/MaxG, Wt/MTOW, Ultimate Load factor)
2. Airbus supercritical wings are VERY aft-loaded.
3. Leading spar only contributes 5% strength - it's more scaffolding for the leading edge

According to one of the pilots of the flight;

Massive crisis mismanagement at Qantas, they seem to be waiting for 11 perfectly good engines to be modified to latest build standard or replaced. Idiots! I would not think for one minute that they are entitled to the special treatment they are demanding. As far as the airline is concerned the engine is a black box – just put the oil in here and push this lever to go forwards – you don’t need to know the build standard, just check the certificate.

All this nonsense to cover their back sides after their really stupid decision to ground everything.

Design flaw?

Source: Accident: Qantas A388 near Singapore on Nov 4th 2010, uncontained engine failure

FF,

Feel better now?


n

Not really, was referring to this article in flightglobal. Thought they must be on about A, B, C builds rafter than software protections.

"Trent 900 shortage keeps Qantas A380s grounded " - but not Lufthansa or SIA

Trent 900 shortage keeps Qantas A380s grounded

FF,

Newspaper articles do not necessarily convey the full story.

My observations are that QF is being responsible.

n

Some pundits are thinking that RR have bigger design issues, causing excessive vibration for example, and incurring greater costs than they are admitting. But I would expect RR to be playing with a straight bat and wish they would put on a press conference to go over all the technical issues to clear the air. Their stock price is holding up pretty well which is a positive sign.

Qantas may well be presiding over one of the most disruptive engine failures in the history of aviation - and that is down to poor decision making and failure to properly assess risks. Partly, Qantas management appears to be muddled by nonsense peddled by ALAEA about risks of outsourcing maintenance and false connection to spline wear going back to early 2010.

20:20 hindsighter at 12 o'clock

first floor

If your post is a "summing up" in an effort to "move on", fair try.

I'll attempt to go the other way. It is a facet of aviation Press/Response that interest dies quickly, perhaps because of technical content. Perhaps other factors. Rolls seems bent on caching this event with other "Lone Defect" incidents, "Whirl Mode", "Skin fatigue", "IPT failure" (2003), etc.

Another look at the "Stub Pipe"?

"Misaligned Counter bore". Fine. What then induced the severe wear on this tube's end? Improper Connection? Incorrect Maintenance? Did the tube fail in service due to fatigue? Or was it Vibration induced by failing IP Shaft Splines?

The Emergency soft-ware "fix" is not a "fix". It is an accelerated warning to interrupt a chain of failure that Remains on the wing? Whereof Lufthansa? How did the Replace/Repair schedule seem to target Qantas for there Naivete? Out of sight out of mind "Engine Maintenance" ?

One dreads the continuation of outsourced Mx, and the loss of stable, and proven domestic care for Aircraft. No reflection on Lufthansa in this case, but Leasing one's Power might need another glance from people other than accountants?

what do you think?

rgds,
bear

A common feature of this incident and the Miami one is crew members trying to look out of the cabin windows to see what has happened and not being able to see anything. Considering how little video cameras cost, would it not be a good idea for cameras to be placed where all engines can be viewed? Recordings from such cameras would have provided useful information both for the crew at the time and for the subsequent investigation.

Shanewhite

An Off Duty Captain flying in back reported seeing a "Fuel Stream" exiting the wing on the Tail Camera feed to his seat. Torn Skin was visible on the Wing's upper surface. The engine's casing was in plain sight. The Casing's shredded state I assume to have been visible. There is a downside to over sampling, especially when it is Human eyes doing the sampling. This could literally have gone either way, and I doubt that the unfolding of events as it happened here, would be trained to the future.

Hindsight is keen, as above, but fraught with opinions that may indicate ways to deal with an unknown that are futile. Uncontained Bursting is not planned for, any provision for its occurrence steps rapidly into the unknown. It is such a potentially lethal situation that it cannot be assessed from a Risk/Benefit position.

Hindsight/Opinion, IMO

On second thought, A barrier against catastrophe is in the cockpit already. A savvy and Experienced Flightcrew. Kudos.

bear

We rely on hindsight; Qantas, Rolls and the rest are working with all the known facts at each stage of the process. Qantas in particular may have been over influenced by the ALAEA briefing against their decision to outsource maintenance in an I-told-you-so fashion.

So ALAEA say things like SIA not safe, Qantas safe…..very safe in fact if they don’t leave the ground!

In principle I see nothing wrong in outsourcing provided you have oversight of the quality of work being done on your behalf. Bear in mind that previous success is no guarantee of future success and as technologies evolve there seems to be a natural tendency for expertise to become concentrated in one place.

First floor

Not really, regarding 11 perfectly good engines, read this.

http://www.flightglobal.com/articles...0-engines.html

Turbine D

First floor

Thanks at least for not being a "me-too" but instead adding more thoughts to the discussion. :ok:

IMO, it is not in RR interest to hold a press conference, instead providing only confirmation of working with the agencies and its customers. It's up to RR to provide a solution first to fully satisfy both the regulator and its customers that "safety" is their first priority and whether the customer is fully satisfied is a busiiness matter.

By accepting the RR recomendations both the regulator and the customer have confirmed RR decsision making and that is all that is needed at this time.

trying to make a suitcase out of a sows ear will only bring out more imaginative pundits

Non-disclosure is a format waiting to be challenged. Thus far, It appears Qantas is keeping open all "Options".

There are TWO HP/IP bearing co-locations. The AD re: the Spline Wear remains in force though I am uncertain as to its "Every Two Cycles" demand.

If the HP/IP co-located bearing structure is the aft (Roller) system, there are no Splines here, meaning that oil problems must have caused a Disc failure unrelated to the AD's language/description: "AFT migration". The possibility then becomes overheat/plastic, friction-caused loss of integrity, then drift into the Stator.

The "secondary" leak referenced in Turbine D's post could mean one in a different location, or a second leak at the failed Stub Pipe of a separate description.

The Wear on this duff pipe is evident and a leak from a compromised connection is assumed, at the least. If at some point the connection failed, the severed system has a different kind of problem, one of an acute nature, rather than merely chronic.

"Misaligned Counter Bore". This is a term that can be used in at least two ways. First, it can describe, as here, a manufacturing mistake.

Secondly, it can describe a poor connection of two lines. It is a parse, but technically correct to use this Phrase to describe merely a poorly connected Oil line.

It does not specify the cause of the "Counter Bore", and wants clarification. The appearance of the Stub Pipe in the image shows only what could be a machining mistake, since all evidence of machine signatures is missing. What is evident in the Photo is Wear, not Tooling.

bearfoil

Did this from the Herald Sun get posted?

FEARS of fuel gushing from ruptured tanks gripped the pilots of the crippled Qantas A380jumbo.
In the first account by a member of the flight crew, senior Qantas check-captain David Evans reveals the most dangerous period during the three-hour drama was during the 50 minutes it took to offload the 469 passengers and crew, reported the Herald Sun.
Even a fire chief at the airport was reluctant to approach the jet because of fears of it exploding from high pressure fuel leaks from the left wing.
Highly flammable kerosene was escaping from a ruptured tank and was pouring on to the brakes, which reached 900C during the landing, Capt Evans said.
Capt Evans had been in the second observer’s seat on the flight deck, running checks on the pilot in command, Capt Richard de Crespigny.
Capt Evans told a British website that when, at 2100m, the No. 2 engine exploded, more than 45 error messages appeared, taking almost two hours to deal with.
“The next thing we were dealing with was the fuel. We had some obvious leaks, some severe, out of the Engine 2 feed tank … there was a fairly significant fuel trail behind the aircraft,” Capt Evans said.
The fuel became imbalanced, the anti-skid brakes were unserviceable, electrical systems failed, and air leaks affected the jet’s hydraulics.
“We lost one of the landing gear computers and once we’d extended the undercarriage using the alternate system we had no indication (at that stage) it was down,” he says.
“We didn’t have the ability to dump fuel, the fuel dumping system had failed and we were about 50 tonnes over our maximum landing weight.
“We had also lost the use of our leading-edge slats, which, consequently with the overweight condition made our approach speed quite fast - 35knots more than normal.
“From then on, it became an exercise in preserving the passengers as best we could.
“We’d lost our satellite phone so the trusty mobile phones came out and we called the company in Sydney to relay back to the company in Singapore, to dispatch some stairs and buses to the aircraft.
“We were 4000m down the end of the runway and it was nearly an hour before we got the first set of stairs to the aircraft and another hour by the time the last passenger departed the aircraft. So it was nearly two hours on the ground with major fuel leaks and engines running.
“I think that’s probably the most serious part of the whole exercise, when you think back.”
He said that with 433 passengers to unload, some elderly and others in wheelchairs, injuries would have happened had emergency slides been used.
“We were lucky enough to get everybody off very calmly and very methodically through one set of stairs,” he said.

ReRun. A different way of describing events, and intended to "dramatize" not truthfully portray. IMO I cannot speak for others, but I recall never being "Gripped with Fear".

regards
bear

fchan
 

You're the only one now talking about "wing replacement". Where did you get that idea from?

It will be repaired, somewhere.

If by "the others" you mean the QF A380s, I think you'll find the answer a few posts above.