Posted on 11/14/2004 4:09:15 PM PST by Clive
HALIFAX (CP) - Investigators in the fatal crash of a massive cargo jet near Halifax have virtually ruled out overloading as the cause and are instead probing the mystery of why the engines were underpowered at takeoff.
Bill Fowler, lead investigator with the Transportation Safety Board of Canada, told The Canadian Press the flight data recorder shows the MK Airlines 747 jet's weight at takeoff was "fairly close to" 352,400 kilograms.
That was the maximum the plane was allowed to weigh for the runway at Halifax International Airport on Oct. 14.
"Bottom line, we do not see at this time that the aircraft was significantly over or under or off the planned weight, based on the math," said Fowler.
The flight data recorder, which was discovered in the wreckage of the crash, indicates what the plane's acceleration and speed were at the time of takeoff.
From this data, mathematical formulas allow investigators with Boeing, the safety board and the National Transportation Safety Board in the United States to determine the mass of the airplane as it lifted off.
Fowler admitted it's still theoretically possible the plane was slightly overweight, but the amount almost certainly wouldn't have prevented a takeoff.
He said the calculations show the plane "was within one per cent, that would mean within 3,500 kilograms" of a planned weight of 350,700 kilograms.
"That (margin) is not very significant in getting an aircraft this size safely off the ground."
Speculation that overloading might have been the cause heightened after the board issued a safety advisory on Oct. 20 that said their probe "raised a concern about the management of loads for cargo flights."
The investigators said they were concerned the weight of seafood on the aircraft had been estimated rather than actually weighed after it was packaged and put on pallets in Halifax.
Fowler said he remains concerned about that practice and the lack of regulatory oversight, but said the investigator's calculations have shifted the probe to the issue of the lack of power at takeoff.
"The big issues is . . . the aircraft took off with the engines set at substantially reduced power from that required to take off at that weight with this runway in those conditions," said the veteran investigator.
The lack of power might have resulted from human error, or mechanical problems with the engines and the systems that control them, he explained.
"What scenario is the most plausible? Is it mechanical? Is it human error? Is there any other system error that might have led to this?"
Deepening the puzzle, the flight data recorder shows the aircraft had a large increase of power just seconds before the plane failed to take off.
"In the latter portion of the takeoff the thrust went up to maximum. We're confident thrust was available," said Fowler.
By then, however, it was too late.
The plane was barely off the ground when its tail struck an embankment 300 metres beyond the runway and broke off.
Fred Chesbro, a pilot and advocate for improved safety on cargo planes, said in an e-mail that investigators should have a close look at the engine settings.
"Some carriers have been known to unwisely suggest to their pilots that they set lower power settings at takeoff and climb in an effort to save wear on the engines," he wrote.
The TSB investigators have noted that two of the cargo jet's four jet engines were replaced just two weeks before the crash and have termed the replacement "unusual."
The company says the replacements were part of routine maintenance.
However, Fowler said that until further documents are obtained from British-headquartered MK Airlines, no further details are available on the reasons for the engine changes.
He's also concerned the destruction of the voice data recorder in the fiery explosion will slow down the investigation because the pilot's final comments aren't available.
Apologies. I omitted the publication date. It is 2004-11-14. There was no byline.
"Some carriers have been known to unwisely suggest to their pilots that they set lower power settings at takeoff and climb in an effort to save wear on the engines," he wrote.
All carriers to my knowledge do this. It's called reduced thrust and it does save wear and tear. Pilots, however, are not generally in favor of the practice.
I would have to say though that given the airplane was at max gross it's unlikely the takeoff was planned using reduced thrust.
I believe they initiated their takeoff at the wrong location on the runway and simply ran out of room. In a panic, the pilot tried to take off thus pulling up hard enough to slam the tail section against the runway, breaking it off. It's my understanding that there is even an eyewitness who stated that they entered the runway to far along.
There was an instance last year of a China Air cargo flight taking off from the parallel taxiway in Anchorage. It had snowed recently and the taxiway had not been cleared to the extent the runway had. They made it but they drug their tires through the snow at the end of their takeoff roll. Tower operators called out the crash trucks as soon as the crew started their takeoff roll (the crew didn't respond to radio calls) so sure were they that they wouldn't make it. Confucious was watching over that crew!
No person is going to risk the aircraft and power down below max tack-off thrust necessary.
Yes, a jet engine can't keep take off power for too long but it is essential for a heavy lift off and those who want to live won't forget it..
From the Fed's mouth to your eyes. Check the link.
Reduced-thrust programs are commonly used and provide significant savings in operating and maintenance costs. Thrust reduction is often controlled using an assumed temperature method, but may also take the form of a "de-rate", in which the aircraft is certified as if the maximum engine thrust is some lower value. "De-rate" methods may permit the operator to use lower values for Vmcg and Vmca, advantageous in conditions of low runway friction. Several manufacturers support the use of "de-rate" thrust on slippery runways.
Despite the many operational benefits of using reduced thrust, there can be significant drawbacks when operating from a contaminated runway. The poor predictability of actual performance in the presence of contamination precludes assuming the additional risk of lower than certified thrust. Variability is compounded when a 15 foot screen height is in use. Lower than expected performance on departure could lead a crew to demand more than the scheduled (reduced) thrust from the engines, and this may in turn lead to control problems.
Thrust reduction, regardless of the method used, may not be employed when operating from a contaminated runway.
http://www.tc.gc.ca/CivilAviation/commerce/manuals/guidance705/division4.htm
Absolutely right!
You'll notice the sentence you quote is in the para. regarding comtaminated runways which says carriers are not to use reduced thrust in those circumstances. Under nomal conditions however, reduced thrust is common.
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