AD 79-21-01 R1 ACTIVE

79-21-01 R1 DETROIT DIESEL ALLISON: Amendment 39-3585 as amended by Amendment 39-4123. Applies to 250-B17, 250-B17B, 250-B17C, 250-C20, 250-C20B, and 250-C20C (MIL. T63-A-720) engines equipped with third stage turbine wheel Part Numbers 6898551, 6898567, 6898733, 6898743, 6898753, 6898763, 6899406, 6899415, 6899416, 6899417, 6899418, 6899419, 6896863, 6898823 and 6899364 installed in aircraft certificated in all categories.
Compliance required as follows unless previously accomplished.
(a) For engines that have previously experienced a hot start beyond the established limits, compliance must be accomplished prior to further flight.
(b) For engines that experience a hot start beyond the established limits after the effective date of this AD, compliance must be accomplished prior to further flight, except that the aircraft may be flown in accordance with FAR 21.197 to a base where the removal can be performed.
To preclude possible engine power loss resulting from third stage turbine wheel blade separation, remove the turbine wheels from service if the following temperature-time limits are exceeded and install an FAA Approved part number turbine wheel.

Temperature Range Time Limit

810 degrees - 927 degrees C. 10 seconds maximum
(1490 degrees - 1700 degrees F.)
Over 927 degrees C. 0 seconds
(1700 degrees F.)

The turbine wheels may not be reworked and reinstalled after a hot start.
NOTE: Time at temperature limits is not additive and may be repeated without restriction.
(Detroit Diesel Allison Commercial Service Letter 1051, Rev. 3, for the 250-B17 series engines and Commercial Service Letter 1084, Rev. 3, for the 250-C20 series engines also pertain to this subject.)
Amendment 39-3585 became effective October 16, 1979.
This amendment 39-4123 becomes effective June 3, 1981.