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ALERT
SUBJECT: THIRD STAGE TURBINE WHEELS, FULL OR CENTER SLlDT BLADE
SHROUDCONFIGURATION, REPLACEMENT AFTER HOT START--SERIES II
ENGINES
The Model 250 Series II engine has experienced blade separation
on third stageturbine wheels of full and center slot (partial)
blade :;hroud configuration.Wheels that have experienced
temperatures in excess of specified limi ts(over-temperature)
during starting, can develop a blade shroud condition thatcan
create a potential for blade failure.I pproval:Continued operation
following a hot start is now orohibited on fullslot crimped and
center (partial)stage turbine wheels on Model 250
slot crimped and uncrimped thirdSeries II engines.
Technical aspects are FAA approved. The
accomplishmentinstructions of Revision 3, or Revision 4 to
thisCommercial Service Letter are approved by the Manager,Chicago
Aircraft Certification Office for compliance withAD 79-21-011 Rl as
indicated.
. Affected Third Stage Wheel part numbers are:UNCRIMPED
CRIMPED689855168985676898733689874368987536898763
689686368988236899364689940668994156899416689941768994186899419
Refer to the Turbine Assembly, Assembly Record (pink pages),
Part V of theEngine Log Book to determine the part number of the
third stage turbine wheelinstalled in your turbine assembly.
July 15, 1979Revision No. 4September 1, 1994250-C20
Series250-617 Series CSL-1084TP CSL-1051Page 1 of 2
Rolls-Royce Proprietary Data Uncontrolled Printed Copy
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ALLISON ENGINE COMPANYCommercial Service Letter
. Time at temperature limi ts during starting are:TEMPERATURE
RANGE LIMITS DURATION LIMITS810'.927C (1490'-1700F) 10 seconds
maximumOver 927C (1700F) Not allowedThe time-at-temperature limits
are not additive and may berepeated without restrictions.
. Required maintenance action in each case is:Send turbine
assembly to an overhaul agency for replacement of theaffected third
stage turbine wheel.
Additional ly, turbine assemblies with these part numbered full
slot crimped andcenter slot crimped and uncrimped third stage
turbine wheels that have a knownor recorded hot start with
temperatures or duration in excess of these limits,should be sent
to an overhaul agency for replacement of the affected thirdstage
turbine wheel.Please make certain that the event, temperature and
duration is recorded in theTurbine Assembly, Service Record (pink
pages), Part I of the Engine Log Bookand that these pages accompany
the turbine assembly to the overhaul agency.
CUSTOMER SUPPORTALLISON ENGINE COMPANY
July 15, 1979Revision No. 4September 1, 1994
250.C20 Series250.B17 Series
CSL-1084TP CSL-1051Page 2 of 2
Rolls-Royce Proprietary Data Uncontrolled Printed Copy
