BA038 (B777) Thread
Airfoilmod,
There are no 'lockouts' that I'm aware of. Selecting alternate mode makes N1 the controlling parameter and this is referenced to the thrust lever position. This means it is possible to exceed the rated thrust of the engine in certain conditions but not overspeed anything; also, the system is designed so that when you switch, you get at least the thrust you had before, possibly more. If you had firewalled before selecting alt. mode, it's very likely one of the the RPM limits would come into play; at much less than TO/GA to begin with you're unlikely to bust anything.
The manual also says: "If the EECs are in alternate mode, advancing the thrust levers full forward provides some overboost and should be considered only during emergency situations when all other available actions have been taken and terrain contact is imminent." Good one to have up your sleeve if you ever need it...
Green-dot,
I really can't see that: all engine parameters were stable and within limits, just not where they wanted them! An engine surge(ing) is difficult to overlook, even from a mile away... Two very different scenarios, IMHO.
snanceki,
I think your comment is pretty much the 'state of the art' at the moment. There are so many possibilities but, like you, I think the probabilities lie here...
...Alt mode is locked out at advanced levers, to prevent over speed, No? Once throttles are retarded and Alt mode select is done, then truly manual Fuel control is obtained.(FAMEC?)
The manual also says: "If the EECs are in alternate mode, advancing the thrust levers full forward provides some overboost and should be considered only during emergency situations when all other available actions have been taken and terrain contact is imminent." Good one to have up your sleeve if you ever need it...
Green-dot,
Could very well be that they perceived engine surging to be their problem at hand at the time.
snanceki,
...as a professional engineer I find it difficult to come to any other conclusion (ON THE INFORMATION AVAILABLE TO US) other than some aspect of the FUEL, conditioned by ENVIRONMENT, and FUEL SYSTEM DESIGN caused a condition that has not been previously considered.
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Loss of fuel system suction feed
From:
Federal Register / Vol. 73, No. 110 / Friday, June 6, 2008 / Proposed Rules.
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA–2008–0618; Directorate Identifier 2007–NM–355–AD] RIN 2120–AA64
Airworthiness Directives; Boeing Model 777 Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
SUMMARY: We propose to adopt a new airworthiness directive (AD) for all Boeing Model 777 airplanes. This proposed AD would require performing repetitive operational tests of the engine fuel suction feed of the fuel system, and other related testing if necessary. This proposed AD results from a report of inservice occurrences of loss of fuel system suction feed capability, followed by total loss of pressure of the fuel feed system. We are proposing this AD to detect and correct failure of the engine fuel suction feed of the fuel system, which could result in dual engine flameout, inability to restart the engines, and consequent forced landing of the airplane.
DATES: We must receive comments on this proposed AD by July 21, 2008.
---- END QUOTE -----
No mention of using any specific grade or type of fuel, or of testing at low temperatures, just testing.
P.S. Many thanks to precept for the link to the US Government AD Notice Search Location in his/her Post #1135 on 13th May, 2008.
Federal Register / Vol. 73, No. 110 / Friday, June 6, 2008 / Proposed Rules.
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA–2008–0618; Directorate Identifier 2007–NM–355–AD] RIN 2120–AA64
Airworthiness Directives; Boeing Model 777 Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
SUMMARY: We propose to adopt a new airworthiness directive (AD) for all Boeing Model 777 airplanes. This proposed AD would require performing repetitive operational tests of the engine fuel suction feed of the fuel system, and other related testing if necessary. This proposed AD results from a report of inservice occurrences of loss of fuel system suction feed capability, followed by total loss of pressure of the fuel feed system. We are proposing this AD to detect and correct failure of the engine fuel suction feed of the fuel system, which could result in dual engine flameout, inability to restart the engines, and consequent forced landing of the airplane.
DATES: We must receive comments on this proposed AD by July 21, 2008.
---- END QUOTE -----
No mention of using any specific grade or type of fuel, or of testing at low temperatures, just testing.
P.S. Many thanks to precept for the link to the US Government AD Notice Search Location in his/her Post #1135 on 13th May, 2008.
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Thanks!
The docket contains more detailed info, such as:
Discussion
We have received a report of in-service occurrences of loss of fuel
system suction feed capability, followed by total loss of pressure of
the fuel feed system. This condition, if not corrected, could result in
dual engine flameout, inability to restart the engines, and consequent
forced landing of the airplane.
FAA's Conclusions
We have determined that it is necessary to require an operational
test of the engine fuel suction feed of the fuel system, and other
related testing, as applicable. Procedures for doing the operational
test can be found in the maintenance manual. The other related testing
is for airplanes on which one or both of the engines stop idling in
less than five minutes after starting the test. Failure of the engine
fuel suction feed of the fuel system could result in the unsafe
condition described previously.
...
Applicability
(c) This AD applies to all Boeing Model 777-200, -200LR, -300,
and -300ER series airplanes, certificated in any category.
Unsafe Condition
(d) This AD results from a report of in-service occurrences of
loss of fuel system suction feed capability, followed by total loss
of pressure of the fuel feed system. We are issuing this AD to
detect and correct failure of the engine fuel suction feed of the
fuel system, which could result in dual engine flameout, inability
to restart the engines, and consequent forced landing of the
airplane.
...
Operational Test/Other Related Testing
(f) Within 7,500 flight hours after the effective date of this
AD, perform an operational test of the engine fuel suction feed of
the fuel system, and perform all other related testing, as
applicable, before further flight, according to a method approved by
the Manager, Seattle Aircraft Certification Office (ACO), FAA. One
approved method is the operational test in Section 28-22-00, titled
``Engine Fuel Feed--General Description,'' of the Boeing 777
Aircraft Maintenance Manual; and Boeing 777 Task Card 28-020-02-01,
titled ``Fuel Feed Manifold,'' dated May 5, 2007. Repeat the
operational test thereafter at intervals not to exceed 7,500 flight
hours.
http://edocket.access.gpo.gov/2008/E8-12691.htm
The docket contains more detailed info, such as:
Discussion
We have received a report of in-service occurrences of loss of fuel
system suction feed capability, followed by total loss of pressure of
the fuel feed system. This condition, if not corrected, could result in
dual engine flameout, inability to restart the engines, and consequent
forced landing of the airplane.
FAA's Conclusions
We have determined that it is necessary to require an operational
test of the engine fuel suction feed of the fuel system, and other
related testing, as applicable. Procedures for doing the operational
test can be found in the maintenance manual. The other related testing
is for airplanes on which one or both of the engines stop idling in
less than five minutes after starting the test. Failure of the engine
fuel suction feed of the fuel system could result in the unsafe
condition described previously.
...
Applicability
(c) This AD applies to all Boeing Model 777-200, -200LR, -300,
and -300ER series airplanes, certificated in any category.
Unsafe Condition
(d) This AD results from a report of in-service occurrences of
loss of fuel system suction feed capability, followed by total loss
of pressure of the fuel feed system. We are issuing this AD to
detect and correct failure of the engine fuel suction feed of the
fuel system, which could result in dual engine flameout, inability
to restart the engines, and consequent forced landing of the
airplane.
...
Operational Test/Other Related Testing
(f) Within 7,500 flight hours after the effective date of this
AD, perform an operational test of the engine fuel suction feed of
the fuel system, and perform all other related testing, as
applicable, before further flight, according to a method approved by
the Manager, Seattle Aircraft Certification Office (ACO), FAA. One
approved method is the operational test in Section 28-22-00, titled
``Engine Fuel Feed--General Description,'' of the Boeing 777
Aircraft Maintenance Manual; and Boeing 777 Task Card 28-020-02-01,
titled ``Fuel Feed Manifold,'' dated May 5, 2007. Repeat the
operational test thereafter at intervals not to exceed 7,500 flight
hours.
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Thanks for the pointer to the docket, it's an interesting read.
However, I don't see its relevance to BA 038.
According to the AAIB's reports ...
So, no suction feed.
If some sort of condition was present on flight BA038 that restricted fuel flow even with the boost pumps operating, why would the FAA propose rulemaking specifically for the case of suction feed?
Bernd
However, I don't see its relevance to BA 038.
According to the AAIB's reports ...
Originally Posted by AAIB S3-2008
[...] the aircraft fuel boost
pumps were serviceable and operated correctly during
the flight.
pumps were serviceable and operated correctly during
the flight.
If some sort of condition was present on flight BA038 that restricted fuel flow even with the boost pumps operating, why would the FAA propose rulemaking specifically for the case of suction feed?
Bernd
Last edited by bsieker; 9th Jun 2008 at 16:23. Reason: Typo.
You might like to refer to my posts, some pages ago, concerning the possibility of trapped air in the fuel suction feed disrupting the fuel supply when released.
Page 28 post 555 para 4. If I knew how to cut and paste, it would be here:
Page 28 post 555 para 4. If I knew how to cut and paste, it would be here:
Last edited by 777fly; 9th Jun 2008 at 16:58.
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Bernd
Just because Boost pumps are operating, does this mean suction feed was not compromised in other ways? The 777 was designed to operate sucking Fuel only, w/o pumps. The cavitation on the High side of the HP engine pumps points strongly to a lack of available Fuel, which means that demand was overpowering supply. To me, this means that the pumps/filters/flow somehow caused the problem, in other words, if the aircraft can run just fine (By Test) at all settings on suction alone, what in addition to suction only would cause the FAA to distribute a Rule that referenced "Dual Flameouts"? AoA? Fuel Viscosity? Fuel Temperature? Sensing Failures? #1 I feel this incident is not complicated, #2 AAIB/FAA have had the solution for some time, #3 Proper time is passing for reasons other than the complexity of the challenge.
Airfoil
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One approved method is the operational test in Section 28-22-00, titled ``Engine Fuel Feed--General Description,'' of the Boeing 777 Aircraft Maintenance Manual; and Boeing 777 Task Card 28-020-02-01, titled ``Fuel Feed Manifold,'' dated May 5, 2007
Usual disclaimers apply!
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There currently is a pressure test carried out at I believe 'A' check level.
So the penny has finally dropped to include the 744.... I wonder why that is
The 744 AMM will require a rewrite to include a vacuum check.
So the penny has finally dropped to include the 744.... I wonder why that is
The 744 AMM will require a rewrite to include a vacuum check.
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To Pool:
Although i agree with you this was an emergency situation and lacked thrust, i was only explaining how the system functions, how the 'hard alternate' mode is designed and operated. Obviously it was not designed with the BA038 incident in mind. Fact remains that there is no thrust limit protection and that is why thrust levers are (partially) retarded if fire-walled and that is how operation in this mode is trained. N1, N2, and N3 overspeed protection remain available. Again, with hindsight, in the case of BA038 none of these limits would probably have been reached. And again with the crew not exactly knowing what was affecting the engines might or might not have followed trained alternate mode procedures, all hypothetical anyway because they had no indication or alert to select the alternate mode and most likely never did.
airfoilmod:
Alternate mode selection does not lock out the thrust levers which, in this case, do not have to be fully retarded to idle and as FullWings explains, in this mode N1 becomes the controlling parameter.
Green-dot
If you're out of thrust, retarding is not necessary.
What if they had firewalled with such a switching? - It would have saved their day, wouldn't it?
This is some silly behind the desk comment. If you are in a emergency situation without thrust, you really don't care about technicalities, formalities, bulletins, sops or similar: Anything that gives you a notch more is very welcome....
What if they had firewalled with such a switching? - It would have saved their day, wouldn't it?
This is some silly behind the desk comment. If you are in a emergency situation without thrust, you really don't care about technicalities, formalities, bulletins, sops or similar: Anything that gives you a notch more is very welcome....
airfoilmod:
Alternate mode selection does not lock out the thrust levers which, in this case, do not have to be fully retarded to idle and as FullWings explains, in this mode N1 becomes the controlling parameter.
Green-dot
Some random thoughts on this AD
It seems to be a data gathering and not a conclusion.
7500 hours does not relate to a confirmed safety of flight situation.
But it is movement in a direction to at least gather pro or con information about a possible problem in a timely manner.
It reminds me of the initial response to the fuse pin issue with the B747 between CI and El Al accidents.
So I will await the inspection results (data vs postulations)
It seems to be a data gathering and not a conclusion.
7500 hours does not relate to a confirmed safety of flight situation.
But it is movement in a direction to at least gather pro or con information about a possible problem in a timely manner.
It reminds me of the initial response to the fuse pin issue with the B747 between CI and El Al accidents.
So I will await the inspection results (data vs postulations)
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FAA Document 2008-0618 URL sources
A direct link to the FAA document regarding 777 suction feed follows. Interested parties may want to click on the imbedded links to both the Docket and to the Document. Comments by the Airlines and interested parties are posted on the Docket response. As can be seen Air New Zealand has already posted comments.
http://www.regulations.gov/fdmspubli...=FAA-2008-0618
http://www.regulations.gov/fdmspubli...=FAA-2008-0618
My knowledge of the 777 fuel system comes from this thread, however, a suction test indicates that the engines are run and the boost pumps switched off, if the engines run down, it would appear that air is entering the system. Air could enter the system from, for instance, a NRV not seating properly. That both engines on BA038 ran down at the same time is still peculiar. This AD addresses the system not the fuel.
It still doesn't make sense, though. With the tank pumps running and the manifold(s) pressurised, fuel is going to leak out rather than air leak in... Unless there was a massive failure of NRVs leading to a kind of short circuit in the fuel supply... But even then, the fuel in the pipes is still at a higher pressure (atmospheric plus a bit of gravity feed) than that at the entry to the engine pumps. 
Still pointing towards some sort of restriction, I feel.
Still pointing towards some sort of restriction, I feel.
If a NRV or PRV is in the system to bleed off excess pressure when the boost pumps are operating, it would not be an external leak when it is working correctly as it is doing the job it is designed for, depending on the pressure it is set at. But if the valve is not seating as it should air can be drawn in from the return line.
Last edited by Oldlae; 10th Jun 2008 at 08:45.
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Any detail on that test ... ?
Turn off APU (to disable APU boost pump)
Switch off all 4 boost pumps.
Engine shall run at idle for 5 minutes.
If not look for leaks in suction feed system.
When I used to do this on the L1011, we did it at take off power. Turned off all the boost pumps at take off and watched that nothing else happened. The engine always continued to run as normal.
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The 7500 hours from publication allowance in the testing requirement suggests a complete lack of any sense of urgency in this inquiry. Cold prospect as far as they're concerned.
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Suction Test
A similar test was called up on the 737-200, much as described by Swedish Steve, but the fuel level had to be quite low, actual figure escapes me, so as to uncover the most of the in tank fuel tubing. The method will work on any aircraft and has been used with success to find holes & bad joints on the in tank fuel tubes.
Last edited by Terraplaneblues; 10th Jun 2008 at 08:21. Reason: Typo