The Bulfer manual tells us that the APU "LOW OIL PRESS" light illuminates during start until the APU oil pressure is normal. However, the Boeing Wiring Schematics I have show that the light is inhibited below 95% and then adds a 20 second time delay for the pressure to rise. This seems to indicate that you will never see the LOW OIL PRESS light unless there is actually a problem with the APU (or perhaps the oil is extremely cold???).Are there any variations between NG APU logic? Have any real pilots/engineers seen this light illuminate during a normal start?Thanks.Cheers.Ian.

Ian ,I can tell you the light illuminates shortly after the switch is moved to start(although it doesn't seem like 20 seconds), it goes out at roughly 30% when monitoring the FMC APU bite page. The light is inhibited with the switch off. The 95% may be for the shutdown mode, because the light does not illuminate on shutdown. I'll try it out monday and let you know.

Thanks, Wallace.Looking forward to your findings.Cheers.Ian.

Ian ,the low oil pressure light comes on immediatly when going to start(or just moving the switch to on).It goes out around 22% rpm.the 20 sec time delay is if the speed is 95%+ and oil pressure is low,the ECU performs an auto shutdown after the 20 sec time delay.

Great stuff, Wallace :-)Engineer "1", Boeing Schematic Diagrams "0" ;-)Cheers.Ian.