Go Back   Airline Pilot Central Forums - Find your next job as a Pilot > >
Technical Technical aspects of flying
 

Welcome to Airline Pilot Forums - Connect and get the inside scoop on Airline Companies

If this is your first visit, be sure to check out the FAQ. Join our community today and start interacting with existing members. Registration is fast, simple and absolutely free.


User Tag List

Reply
 
Thread Tools Search this Thread Display Modes
Old 09-04-2008, 08:58 PM   #1  
Moderator
Thread Starter
 
vagabond's Avatar
 
Joined APC: May 2006
Position: C-172
Posts: 7,653
Default AAIB Report On Boeing 777-236ER

Not sure if this has been posted before. I did try to read the report, but it's too techie for me and I have only a headache to show for it. No comprehension at all.

Quote:
From Associated Press:
DALLAS U.S. regulators will tell airlines to quickly make changes aimed at preventing ice from building up in fuel lines of Boeing 777s, which British investigators said today probably caused one of the jets to make a jarring emergency landing last January in London.

The Federal Aviation Administration's formal directive by week's end will require changes in the way ground crews prepare planes and pilots fly them in extreme cold weather, FAA spokeswoman Alison Duquette said today.

Currently 777 pilots are required to rev their engines when the fuel temperature falls to 14 degrees Fahrenheit. That would conceivably dislodge any ice that might be in the fuel line.

The FAA directive will apply to more than 50 U.S.-registered Boeing 777s with Rolls Royce engines, mostly operated by American Airlines and Delta Air Lines.

FAA spokesman Les Dorr said the directive is viewed as an interim measure, and Rolls Royce will be expected to make design changes to its engines.

The U.K. Air Accidents Investigation Branch recommended that the FAA and European regulators immediately consider whether the same problem could occur in planes with different engines a move that could affect many more carriers.

Duquette said, however, that the FAA's initial review "has not revealed the same vulnerability to ice buildup in the fuel lines" of Boeing 777s with different engines.

The report by the British investigators also recommended that regulators review certification requirements to make sure fuel systems can cope with possible ice buildup.

The investigators said water normally present in aircraft fuel probably froze in the fuel lines and caused a British Airways jet to lose power and make an emergency landing just inside the Heathrow Airport boundary on Jan. 17. More than a dozen people suffered injuries, including one listed as serious.

The flight from Beijing had been uneventful until its final approach. Just 720 feet above the ground, the jet began losing power in the right engine and, seven seconds later, in the left one, investigators said in a report issued today. They said those events were consistent with a drop in fuel flow.

"Although the exact mechanism in which the ice has caused the restriction is still unknown in detail, it has been proven that ice could cause a restriction in the fuel feed system," the report said. "The risk of recurrence needs to be addressed in the short term whilst the investigation continues."

The report called for the FAA and the European Aviation Safety Agency to work with Boeing and Rolls-Royce to develop measures to reduce the risk of ice forming.



Jim Proulx, a Boeing spokesman, said the company was recommending several procedural changes and a new checklist for operators of 777s with Rolls Royce engines about 30 percent of the 736 planes in service.

American Airlines operates 47 Boeing 777s with Trent engines. The nation's largest airline had no immediate comment on the British findings.

Delta spokeswoman Betsy Talton said the airline flies 10 777s, all with Trent engines. She said the airline would comply with any safety directive from the FAA.

Boeing's Proulx said 777s with Pratt & Whitney engines are designed differently and do not seem prone to ice buildup. United Airlines flies 52 of those, and Continental Airlines has 20.

The Rolls Royce Trent 800 engines have fuel oil heat exchangers that cool engine lubricating oil and warm fuel to prevent the formation of ice.

However, there are no regulatory requirements that address the possibility of a sudden release of a large amount of ice, which could disrupt fuel flow.

Ice crystals start to form when the fuel temperature dips to 31 to 27 degrees Fahrenheit, but generally remain suspended as discrete particles, the report said. At 0 degrees Fahrenheit, the crystals can stick to each other and form clumps.

The investigators said little is known about the mix of ice crystals and fuel at even colder temperatures they called for further research.

The fuel temperature during the Beijing-London flight fell to minus-29 degrees Fahrenheit for 80 minutes as the outside air temperature at high altitude dipped to 49-below, investigators said.

The National Transportation Safety Board in Washington said it supported the recommendations made by the British aviation-safety agency. NTSB acting chairman Mark Rosenker said the investigation shows that international cooperation can lead to safety improvements.

This is the AAIB report.
vagabond is offline   Reply With Quote
Old 09-08-2008, 10:39 AM   #2  
Gets Weekends Off
 
DamonMeyer's Avatar
 
Joined APC: Aug 2007
Position: Ramen-eating duck driver
Posts: 252
Default

Why can't the water be sumped out of jet fuel either before or after it's put in the plane...? If that's answered in the AAIB report, just slap me and I'll go read it (as appetizing as it sounds, from Vagabond's description).
DamonMeyer is offline   Reply With Quote
Old 09-08-2008, 10:57 AM   #3  
Gets Weekends Off
 
joepilot's Avatar
 
Joined APC: Jul 2008
Position: 747 Captain (Ret,)
Posts: 619
Post

Quote:
Originally Posted by DamonMeyer View Post
Why can't the water be sumped out of jet fuel either before or after it's put in the plane...? If that's answered in the AAIB report, just slap me and I'll go read it (as appetizing as it sounds, from Vagabond's description).
Water can remain suspended in jet fuel, especially when it is warm. It doesn't seperate out nicely like it does from gasoline. When the fuel gets cold you can get little water ice particles, but the real problem is that when the fuel gets really cold, like -45 to -50 centigrade, the fuel itself can start to freeze. It turns waxy, or like cold grease.

Joe
joepilot is offline   Reply With Quote
Old 09-08-2008, 11:24 AM   #4  
Gets Weekends Off
 
DamonMeyer's Avatar
 
Joined APC: Aug 2007
Position: Ramen-eating duck driver
Posts: 252
Default

Quote:
Originally Posted by joepilot View Post
Water can remain suspended in jet fuel, especially when it is warm. It doesn't seperate out nicely like it does from gasoline. When the fuel gets cold you can get little water ice particles, but the real problem is that when the fuel gets really cold, like -45 to -50 centigrade, the fuel itself can start to freeze. It turns waxy, or like cold grease.

Joe
Do they use PRIST in the 777? If so, is there some fuel system design difference in the Boeing that negates it's properties...?
DamonMeyer is offline   Reply With Quote
Old 09-08-2008, 12:02 PM   #5  
Prime Minister/Moderator
 
rickair7777's Avatar
 
Joined APC: Jan 2006
Position: Engines Turn Or People Swim
Posts: 22,404
Default

I don't think airliners use PRIST.

Bulk fuel freezing is not the problem...the bulk fuel is not allowed to get that cold ( -40 for normal jet A). Fuel recirculation and/or dumping heat from other systems keeps it well above that.

But on long, high-altitude flights fuel can get cold enough to freeze water. Like somebody mentioned, there is always some trace amount of water...unless the fuel is allowed to sit undisturbed for an extended period (days?) the water will not seperate out.

The real issue appears to be a combination of a very long, unusually cold flight, and some design feature of the 777 fuel system which can allow the build-up of suspended ice crystals at a flow-restriction point under certain circumstances.

It's also possible they got fuel with higher-than-normal water content which would have aggravated the siuation.

The 777 has been flying for well over a decade now...I suspect it would take a very precise combination of circumstances to repeat this incident.
rickair7777 is offline   Reply With Quote
Old 09-08-2008, 12:21 PM   #6  
Gets Weekends Off
 
joepilot's Avatar
 
Joined APC: Jul 2008
Position: 747 Captain (Ret,)
Posts: 619
Post

On a long range polar flight, with the OAT below -70 Centigrade, I have seen the fuel temp guage measure below -40 in an outboard tank.

Joe
joepilot is offline   Reply With Quote
Old 09-09-2008, 04:14 PM   #7  
Prime Minister/Moderator
 
rickair7777's Avatar
 
Joined APC: Jan 2006
Position: Engines Turn Or People Swim
Posts: 22,404
Default

Quote:
Originally Posted by joepilot View Post
On a long range polar flight, with the OAT below -70 Centigrade, I have seen the fuel temp guage measure below -40 in an outboard tank.

Joe
There are different vedrsions of jet A for that sort of flying, I assume you use one. Standard domestic Jet A is supposed to gell at -40C.
rickair7777 is offline   Reply With Quote
Old 09-09-2008, 05:57 PM   #8  
Gets Weekends Off
 
ryguy's Avatar
 
Joined APC: Mar 2006
Position: B777 FO
Posts: 414
Default

They would have been fueled with Jet-A1 in China which has a freeze point around -47C. The problem looks to be that the left over fuel from the aircraft's flight to N. America mixed, causing an overall higher freeze point.
ryguy is offline   Reply With Quote
Old 09-09-2008, 08:16 PM   #9  
Gets Weekends Off
 
joepilot's Avatar
 
Joined APC: Jul 2008
Position: 747 Captain (Ret,)
Posts: 619
Post

Quote:
Originally Posted by rickair7777 View Post
There are different vedrsions of jet A for that sort of flying, I assume you use one. Standard domestic Jet A is supposed to gell at -40C.
Hi Rick

We use standard Jet A. I agree that the minimum specification fuel freeze (gel) point is -40 C. However most fuel actually exceeds the specification, and freezes at a lower temperature. Prior to each polar flight a sample of the actual fuel boarded is taken to a lab, and the actual freeze (gel) temperature is determined. We then use the actual fuel freeze temp plus 3 degrees C as our in flight fuel temp limit. If fuel temp approaches the limit, it may be necessary to change to a warmer altitude or increase Mach to get a warmer temp.

Joe
joepilot is offline   Reply With Quote
 
 
 

 
Reply
 



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Related Topics
Thread Thread Starter Forum Replies Last Post
Boeing Fires CEO Stonecipher SWAjet Major 0 03-07-2005 09:48 AM


All times are GMT -8. The time now is 02:43 AM.


vBulletin® v3.9.3.5, Copyright ©2000-2019, MH Sub I, LLC dba vBulletin
User Alert System provided by Advanced User Tagging v3.3.0 (Lite) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Website Copyright 2000 - 2017 MH Sub I, LLC dba Internet Brands

Search Engine Optimization by vBSEO 3.6.1