The APU also provides mechanical power in the form of rotational shaft power to drive a generator which provides electric power to aircraft systems. During final acceptance testing the 36-150[FN] and 36-150[G] APU’s may experience combustion instability or a lean blowout at the bleed air transient test point. The bleed air transient test point is the point at which the bleed air load is removed from the APU by closing the load control valve.
The current dimensional tolerances allow for too much variation during the manufacturing of the combustor, P/N 3830450-2. This variation can cause the dome deflector position to change too much relative to the combustor cooling holes. A combustor manufactured with the dome deflectors on the extreme high or low side of the tolerance may cause a lean blowout of the APU during final acceptance testing.
A new combustor has been developed, P/N 3830450-3, which better controls the position of the dome deflectors resulting in improved combustion stability and a robust primary combustion zone eliminating the lean blow out condition. The new combustor will be introduced via Service Bulletin GTCP36-49-8101
GTCP36-49-8101 Revision 0, Anticipated Released date is March 2013