Just a quick question, Boeing 737-8xx 's APU (Garret or Sundtrand) panel, you have only the EGT monitoring. IS there any way to check the RPM? as to know the APU load?
Without going into the CDU, no. You can get a idea of the RPM by watching the APU generator freq's.
when you start the engines by using the APU bleed, the duct pressure shows 19psi (because the APU is idle!) but when the ground switch moves to GRD position of the engine, the Duct pressure rise to about 35-40psi as the APU is now loaded.
Theoretically the APU doesn't ever idle, it runs at a constant speed whether unloaded or loaded. You could have a full generator load on the APU and you will still have the 19psi with APU bleed air selected but no bleed air demand. This APU has a separate load compressor with IGV's that control the pressure. So when the eng. start switch is moved to ground, the APU ECU commands the IGV's to open to allow the load compressor to increase air pressure/volume.
What would be the starting sequence for APU bleed induced engine start?
When start sw. is moved to ground, the start valve opens, IGV's open, air is supplied to the starter, starter turns the N2 rotor, at 56% N2 the start switch returns to off/auto, start valve closes, starter disconnects (through a sprag clutch) IGV's close, duct pressure returns to unloaded pressure.
But generally do you keep the BITE page open on the FMC every time you powering up the engines? and is that the way to monitor the RPM on NGs?
No and (APU RPM) yes.
When starting the APU no RPM monitoring?
Not normally. I only watch RPM when troubleshooting.
If a moment you can think that the NGs fixed with Sundstand APU's are FADEC ~ ECB controlled hence lets say there is no very much of a requirement for a RPM indication, but how about in classics and originals? do they have ?
No RPM indication on the jurassic and classic. There is test equipment we can use to monitor RPM, but normally any adjustments made to the RPM is done to attain the desired generator frequency, so we don't usually care what the actual RPM is.