Thu, Dec 14, 2006
Switching Types Led To Coke Formation In A330's Turbines
In its latest round of
recommendations for the Federal Aviation Administration, the
National Transportation Safety Board on Thursday asked the FAA to
amend its guidelines for engine oil use, and inspections when a new
type of oil is used.
The recommendations come after an Edelweiss Air Airbus A330-200
experienced an uncontained turbine blade release from its No. 1
(left) Rolls-Royce Trent 772-60/16 turbofan engine, while climbing
through FL230 after departing from Miami International Airport in
October 2003. The flight crew declared an emergency and returned to
Miami, where the pilots successfully landed the airplane. No
injuries to the 12 crewmembers or 171 passengers were reported.
While the NTSB says the engine fire made it nearly impossible to
examine the No. 1 engine, a borescope inspection of the No. 2
engine revealed the HP/IP turbine bearing chamber internal vent
tube was obstructed with a black substance, later determined to be
nodules of carbon deposits (also known as coke) left from the
engine's lubricating oil. Such nodules aren't uncommon, but the
engine showed a much greater amount of deposits than was considered
normal.
Investigators then learned the airline had recently changed
engine oil types... and the pieces started to fall into place.
Based on its findings, the NTSB recommends the FAA:
- Revise Advisory Circular (AC) 20-24B to include guidance to
ensure that each time a new engine/oil combination is introduced,
procedures are developed and implemented to inspect, at appropriate
intervals, those areas within the engine where testing or
in-service experience has indicated porous carbon formation is
likely and has the potential to result in hazardous oil system or
engine behavior. AC 20-24B should also provide criteria for
evaluating the results of these engine inspections to aid operators
in determining whether continued operation is safe or whether the
engine/oil combination should be discontinued. (A-06-85)
- Review the maintenance programs for all engine and oil
combinations currently in service, with particular emphasis on the
evaluation of airplanes approved for extended-range operation with
two engines, to determine that operators have gathered and
evaluated sufficient data, including operational experience and
engine hardware disassembly inspection findings, to ensure that
these combinations are not at risk of producing potentially
hazardous porous-coke conditions. If such data do not exist or are
insufficient, require operators to implement appropriate measures,
including periodic inspections, to collect and evaluate the
necessary data until the safety risk associated with the presence
of porous coke is either ruled out or properly controlled.
(A-06-86)
- Coordinate with international regulatory agencies to inform
them of the circumstances of the event involving Edelweiss Air
flight EDW 565 and to encourage them to develop and adopt
comprehensive standards and procedures regarding the introduction
of new engine/oil combinations, including the inspection at
appropriate intervals of those areas within the engine where
testing or in-service experience has indicated porous carbon
formation is likely and has the potential to result in a hazardous
engine condition. This coordination effort should also ensure that
sufficient data, including operational experience and engine
hardware disassembly inspection findings, have been gathered and
analyzed, with particular emphasis on airplanes approved for
extended-range operation with two engines, to support continued
operation of engine/oil combinations. (A-06-87)
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