The  engine  starting  systems for  DC-9 and MD - 80 airplanes have collectively experienced 11 reported uncontained starter failures since 1978. As the result of an event that occurred in April 1995, it has been determined that some engine start valves may be blown open when subjected to engine 13th stage high pressure bleed air greater than 260 psig. The engine starting system experiences these pressure levels when a pneumatic system augmentation valve fails in the open position or when conducting high pressure pneumatic system testing per Maintenance Manual chapters 21 and 36 procedures.

The fact that some start valves may be blown open is not detrimental in itself when the condition occurs with a regulated start valve, P/N 392796-X, because the starter turbine will be propelled by bleed air regulated at less than 50 psig. However, when the condition occurs with a non-regulated start valve, P/N 979410-X, (actually install in Spanair MD’s) installed, the starter turbine is also driven by the same level of pressure that blew the valve open. Comparatively, it has been demonstrated that a starter turbine running in a free-wheel state with regulated bleed air (50 psig) will run at least five minutes, while a turbine driven by non-regulated bleed air can fail in approximately one and one half (1.5) minutes. The five minute duration is important since it allows the pilot sufficient time to take corrective action as specified in the FCOM, which is to reduce engine power, preventing starter failure.

During airfoil ice protection selection the crossfeed valves are open. The maximum supply pressures associated with ambient conditions under which ice protection is selected is 235 psig. Starter valve testing indicated the lowest pressure at which the valve will open is 260 psig. Therefore, it can now be concluded that a starter failure caused by a failed open pneumatic augmentation valve during ice protection cannot occur.

The engine start valves are wired to provided an open indication in the cockpit on the overhead panel that will illuminate or annunciate any time the valve is at least five degrees open (START VALVE OPEN). During airfoil anti-ice operation, should a pneumatic system augmentation valve fail open, a master caution light will illuminate and a left or right ice protection temperature high (L/R ICE PROT TEMP HIGH) annunciation will occur in 12 to 15 seconds. In addition, during non-icing conditions the air conditioning supply temperature high light (L/R AIR COND SUPPLY TEMP HI) and a master caution will be illuminated with a failed open pneumatic augmentation valve during takeoff. The procedures for these three abnormal conditions exist in the flight crew operating manuals (FCOM), MD-80 FCOM, Volume II, Section 3, Items 7-30-5, 12-30-0 and 2-30-0, and DC-9 FCOM, Section 2, Items 30-15-1, 50-15-0 and 45-15-0. Flight crews may wish to review these three operating procedures.

Although Douglas delivers aircraft with regulated start valves, some operators have modified the start valves to remove the pressure regulating feature by incorporating alliedsignal service Bulletin 392796-80-1249. Douglas provided a no technical objection in AOL 9-1242 to this de-regulating; however, after learning that the start valves may be blown open, Douglas retracted the no technical objection by issuing AOL 9-1242A and requested that operators discontinue de-regulating the start valves.

It should be noted that four of the 11 starter events resulted in fires. The fires were the result of oil and/or fuel contacting the hot pneumatic components/fragments. Fragments from the starter turbine have penetrated oil and fuel lines which can feed the fires. The right hand (No. 2) engine can be more susceptible to fuel line punctures because the fuel feed line is in the vicinity of the engine starter.

As a result of the above:

1. Douglas issued AOL 1242A to retract the no technical objection regarding the de-regulation of the start valves. The Douglas position is that the regulated start valve is the superior configuration.

2. Douglas issued temporary revisions to DC-9 and MD-80 Maintenance Manuals, Chapter 21 and 36, to Limit the Test/Operating pressures to 45 psig. Subsequent temporary revisions have been issued to increase the pressures to 200 psig provided that an observer is used to monitor the start valve annunciators/lights when using high pressure bleed air.

3. It has been determined that the non-regulated start valve, P/N 979410-X, should be modified. This can either be accomplished by incorporating alliedsignal service bulletin 979410-80-1611, dated November 27, 1995, which reinstalls the pressure regulating feature, or incorporate the alliedsignal service bulletin to install the improved control solenoid that will preclude the valve from being blown open. The improved solenoid service bulletin and parts are tentatively scheduled to be available in the third quarter of 1996.

4. Douglas has conducted qualification testing of axial containment devices for the engine starters: The integral device incorporated by alliedsignal service Bulletin 383342-80-1554 or production equivalent starter, P/N 383342-14, has been requalified; Clamp on device, P/N 65C13014-1, installed by Douglas service Bulletin 80-6 and in production for fuselage numbers 905 through 2076 has been requalified; and clamp on device, P/N 65C13014-3, has been newly qualified. In addition, clamp on device, P/N MTM94016-103, manufactured by may tool and mold company has been accepted as an equivalent to the other clamp on devices.

Not included in the above but important to operators, alliedsignal service Bulletin 383342-80-1619, to drill the hole through the tripod bumper for starters, P/N 383342-14, to facilitate engine rotation during borescope inspections, should be released by the end of May 1996.

It is requested that this information be disseminated, as a minimum, to all appropriate personnel in flight operations, engineering and maintenance.