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Guest Sirocco

737-500 questions

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I have some questions on the 737-500. What do these indicators mean?A/P P/RSTA/T P/RSTFMC P/RSTI know it's autpilot, auto throttle and, well, FMC, but "P/RST" and what to do about each one remains a mystery.And what is "cabin alt"? How do you define the value to set it at?

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The "P" stands for pitch. The "RST" stands for receiver/sensor/transmitter. Thus input for the autopilot, auto-throttle, and flight management computer."cabin alt" stands for cabin altimeter. This gauge helps the crew monitor cabin pressurization so that the cabin does not exceed maximum allowable differential pressure.fb

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Thanks for your reply.>The "P" stands for pitch. The "RST" stands for>receiver/sensor/transmitter. Thus input for the autopilot,>auto-throttle, and flight management computer.The first two were flashing, the third was steady. What does that indicate?>"cabin alt" stands for cabin altimeter. This gauge helps the>crew monitor cabin pressurization so that the cabin does not>exceed maximum allowable differential pressure.I'm puzzled here. What's the difference between landing and cabin altitude?

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Flashing lights on any of these indicators probably means that the pressure had not stabilized within one of the sensors - perhaps during engine startup.Not sure what you mean by "landing" altitude but I would guess you're referring to the altitude pressure measurement at the point of touchdown. The other pressure indication has to do with cabin pressure regardless of the outside pressure.fb

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>Not sure what you mean by "landing" altitude but I would guess>you're referring to the altitude pressure measurement at the>point of touchdown. The other pressure indication has to do>with cabin pressure regardless of the outside pressure.They're on the pressurisation panel. I've read one or two explanations that seem to indicate they're the same thing, but why have two fields?

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Cabin alt is the pressure altitude of the cabin at the moment.Landing alt is used by the automatic pressurisation system to ensure the cabin is pressurised to the airfield elevation at the point of landing. i.e. there are no unpleasant pressurisation fluctuations when the outlet valve is driven open after landing.The landing alt is an input field, set by the pilots sometime before descent, the cabin alt merely indicates the current alt of the cabin.Hope this helps,Ian

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>The "P" stands for pitch. The "RST" stands for>receiver/sensor/transmitter. Thus input for the autopilot,>auto-throttle, and flight management computer.>>Flashing lights on any of these indicators probably means>that the pressure had not stabilized within one of the sensors>- perhaps during engine startup.>Ermmm... not correct at all to be honest ;)The first one (AP P/RST) is the autopilot disengage light and will flash when the autopilot has disengaged.To reset the flashing light press the autopilot disengage switch on the yoke a second time or simply press the annunciator light itself (hence P/RST = push to reset)AT P/RST is the autothrottle disengage light which will flash when the autothrottle has disengaged.Push to reset the light or press the AT disengage on the throttles a second time.Finally FMC P/RST is called the FMC alert light and indicates an FMC message is displayed on the scratchpad of both CDUs.You guess it... press to reset :-) or clear the message in the scratchpad with the CLR key.Regards,Sylvain

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>The landing alt is an input field, set by the pilots sometime>before descent, the cabin alt merely indicates the current alt>of the cabin.Ah. That makes sense. Thanks.

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>The first one (AP P/RST) is the autopilot disengage light and>will flash when the autopilot has disengaged.>To reset the flashing light press the autopilot disengage>switch on the yoke a second time or simply press the>annunciator light itself (hence P/RST = push to reset)>>AT P/RST is the autothrottle disengage light which will flash>when the autothrottle has disengaged.>Push to reset the light or press the AT disengage on the>throttles a second time.>>Finally FMC P/RST is called the FMC alert light and indicates>an FMC message is displayed on the scratchpad of both CDUs.>You guess it... press to reset :-) or clear the message in the>scratchpad with the CLR key.I was halfway there, pushing the lights to turn off the warnings. But it's good to learn what they were telling me.

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