Investigation has revealed that the starter valve may not sustain the high pressure which is applied if an augmentation valve failure occurs. (Stuck in open position due to a sense line failure.)

With the onset of the winter season where airfoil anti-icing procedures would be required, concern grew because of the possibility that both engine starters could simultaneously be affected by exposure to high pressure 13th stage bleed air. (Airfoil -A-ice on, both x-feed valves open). This could occur by the high pressure air forcing the start valve solenoid ball off its seat for one or both starter valves, An analysis of the system pressure under anticipated worst case operating conditions did not prove or disapprove the two-starter possibility, however, if one starter valve opens, the subsequent pressure drop in the pneumatic manifold will be at such a valve that the possibility of blowing open the second starter valve is very remote.

Should the starter fail uncontained (burst), particularly on the right-hand engine it is possible that a fire could be the result. The right-hand engine is mentioned specifically because there is a fuel line in close proximity to the starter.

Here are some facts that relate to time. When an augmentation valve fails open and the crossfeed valve is open, it takes 12 to 15 seconds for the master caution light and the “ICE PROT TEMP HIGH” or the “Air cond supply temp hi” annunciation to illuminate. Both warnings are connected to the master caution circuit. The “START VALVE OPEN” annunciation will illuminate as soon as the valve opens. The start valve position is not connected to the master caution circuit, however, this warning deserves first priority for immediate action. It has been demonstrated in service and under controlled testing that unregulated high pressure bleed air driving the starter in a free wheel state will cause the starter to fail in approximately 1 minute and 15 seconds to 1 minute and 28 seconds.

The problem will be solved by MDC by creating a new solenoid, strong enough to sustain pressure up to 250 psi. Until the hardware change is done, we recommend the following procedure especially during high power setting as TO and GA:

In case one of the mentioned warnings illuminate, switch off the airfoil system immediately and close both crossfeeds if conditions permit.