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Paul12

Buzzer sounds when aircraft is located at high altitude airports

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I parked the PMDG-737 at LaPaz,Bolivia which has an altitude of 4000 meters.

Before I could do anything I got a buzzer sound,after that I parked at an airport with

3310 meters,same result.

Finally I went to an airport of 2900 meters altitude and there was no buzzer sound anymore.

 

Can anybody explain why and also how to stop the buzzer sound.

 

HubertWerni

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I parked the PMDG-737 at LaPaz,Bolivia which has an altitude of 4000 meters.

Before I could do anything I got a buzzer sound,after that I parked at an airport with

3310 meters,same result.

Finally I went to an airport of 2900 meters altitude and there was no buzzer sound anymore.

 

Can anybody explain why and also how to stop the buzzer sound.

 

HubertWerni

 

Maybe your doors are open and it is detecting you are over 10,000 feet with an oxygen problem. 

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The buzzer you’re hearing is a high cabin altitude warning.  Normally for operations into airports above 10000’ you’d want a 737 equipped with a high altitude landing switch which raises the warning altitude from 10000’ to 14000’.

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Maybe your doors are open and it is detecting you are over 10,000 feet with an oxygen problem. 

 

Maybe your doors are open and it is detecting you are over 10,000 feet with an oxygen problem. 

Hello,

I was thinking of that too,therefore I checked the doors,all of them were closed.

The buzzer you’re hearing is a high cabin altitude warning.  Normally for operations into airports above 10000’ you’d want a 737 equipped with a high altitude landing switch which raises the warning altitude from 10000’ to 14000’.

OK,how can  I equip my 737 with a high landing switch or is it built in and I have to make some adjustments.

Thanks

 

HubertWErni

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OK,how can I equip my 737 with a high landing switch or is it built in and I have to make some adjustments.

 

Just silence the alarm.  The ALT HORN CUTOUT switch is overhead.  However, consider that the simulated aircraft has the limitations as outlined in FCOMv1 specifically maximum of 8400 ft (2560 m).

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I landed at La Paz Altiplano (13,800 ft.) once. As Dan says the cabin altitude is about 8,000 feet and normally you depressurize to a lower level. We had to wait a while before opening the aircraft doors and the captain said something about the cabin pressure. In this case the airport is higher altitude than the cabin altitude. You don't want to open the doors with a pressure difference that's a big no no. That is why you have that horn. Can you operate the cabin pressure manually to that level ?

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Can you operate the cabin pressure manually to that level ?

 

I guess you could but why? Set the landing altitude in the pressurization controller panel to landing elevation or slightly above. The range for LAND ALT is -1000 to 14000 see FCOM pg 2.10.13

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Oh yes normally that is what you would do, but if you skipped the step for whatever reason and had already landed .......

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I landed at La Paz Altiplano (13,800 ft.) once. As Dan says the cabin altitude is about 8,000 feet and normally you depressurize to a lower level. We had to wait a while before opening the aircraft doors and the captain said something about the cabin pressure. In this case the airport is higher altitude than the cabin altitude. You don't want to open the doors with a pressure difference that's a big no no. That is why you have that horn. Can you operate the cabin pressure manually to that level ?
I believe most airplanes have a negative pressure release valve that prevents the cabin altitude being lower than the surrounding environment.

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I believe most airplanes have a negative pressure release valve that prevents the cabin altitude being lower than the surrounding environment.

If the cabin alt is lower than the outside, then it's a higher pressure. The negative relief valve wouldn't do a thing.

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I believe most airplanes have a negative pressure release valve that prevents the cabin altitude being lower than the surrounding environment.

 

The cabin altitude should be lower than the surrounding environment.  That's the whole point of pressurization.

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The Chancellor dumps pressurization by opening the outflow when the main gear squat switch closes... big iron have anything like this?

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Wes is correct but he just got it backwards, there is a negative pressure relief valve that prevents outside pressure being higher than the cabin.  It’s just a spring loaded door that lets air in if the pressure outside is higher.  As for the outflow valve, yes it goes to full open on the ground via the air/ground sensor.  The application of power on takeoff is the signal for the valve to start modulating for pressurization.  

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As for the outflow valve, yes it goes to full open on the ground via the air/ground sensor.

The outflow valve won't open fully on the ground if the cabin is still pressurised. It will open a small amount, the cabin rate of climb is limited to a safe level. It opens fully when the cabin differential pressure is within limits.

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On 2/19/2016 at 7:46 PM, kevinh said:

 

 

The outflow valve won't open fully on the ground if the cabin is still pressurised. It will open a small amount, the cabin rate of climb is limited to a safe level. It opens fully when the cabin differential pressure is within limits.

So do we have to manually adjust the pressure or just wait until the diff goes within limits?

-Angelo Busato

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You don’t have to do anything manually. Just let the pressure controller do its job. 

  • Upvote 1

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