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instrument problem

Guest

im flying a boeing 737-400 from london to moscow, ive just entered russia and my altimeter and airspeed indicator seem to be malfunctioning. a moment ago my airspeed indicator read 565 kts and noe says 383, but there seems to no adverse affects on the plane and no g force. My altimeter went from 32000ft (my cruising altitude ) to 13000ft then as i tried to climb and reduce speed it said 2600ft, it now reads NEG560. It looks as if i am at my correct altitude but i cant be sure. This is the first time i have encountered such problems, can anyone advise me on what to do?

Pro Member First Officer
Jamie Robson (Jamier) First Officer

is pitot heat on? otherwise declare emergency and land asap!

Pro Member Chief Captain
pilotwannabe Chief Captain

You may have entered sever turbulence...try climbing out of it Wink

Make sure you check your pitot heat as Jamier suggested though Wink

Pro Member First Officer
davidmac1 First Officer

sorry, that was me who posted the original message. pilot heat was off. I declared an emergancy and changed my ifr destination to minsk-1. I turned and followed atc instructions but i couldn't use my autopilot to descend because it was as confused as i was, when i got nearer to minsk the instruments seemed to be back working fine, although my altimeter still read a couple of thosand feet to high so i relied on the aircrafts automated messages to get me down, it turned out to be a perfect landing! In my flight report the passengers thought that it was an exeptional flight (100%) But it said that i declared what seemed to be a false emergancy! Its ok, as long as i didn't crash! the only problem ios, it was for my va, so i've just wasted all that time on nothing really!

BTW thanks for the advice!

Pro Member Chief Captain
pilotwannabe Chief Captain

Yeah...it sounds as though your pitot's froze over, hence why things started working agin in lower, warmer air. Congrats on your perfect emergency landing though Wink

Pro Member First Officer
Jamie Robson (Jamier) First Officer

yep, congrats, as long as its a safe landing its worth it Smile

Pro Member First Officer
PH First Officer

Question....why would pitot freezing affect the altimeter?

Pro Member Chief Captain
pilotwannabe Chief Captain

PH wrote:

Question....why would pitot freezing affect the altimeter?

Becasue the pitot-static pressure system provides the values for

-Altimeter
-Vertical speed indicator
-Airspeed indicator

Wink

Pro Member First Officer
PH First Officer

Let me rephrase.....what does the altimeter rely on, pitot or static?

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

pilotwannabe wrote:

PH wrote:

Question....why would pitot freezing affect the altimeter?

Becasue the pitot-static pressure system provides the values for

-Altimeter
-Vertical speed indicator
-Airspeed indicator

Wink

PW,

I think the pitot tube measures speed and the static port measures altitude. Yes the pitot tube does measure static and dynamic pressure to work out the total pressure - with the air density and different pressures worked out by the Pitot Tube then Bernoulli's equation can be used to work out speed. It is called the Pitot-Static tube sometimes because it works out static and dynamic pressure in order to work out the speed.

The static port is a small hole in the plane (bit of a crude definition) which is connected to the altimeter which determines airpressure and then altitude. There are often 2 (one on each side) to balance out differences in readings from the effects of the sideslip. I think you have the two devices confused.

I think thats right, but PH can confirm or correct me.

Pro Member Chief Captain
pilotwannabe Chief Captain

I think your probably right Jon Wink

Thanks for correcting me Thumbs Up!

So what caused davemac1's original problem??

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

Its hard to say.

It doesn't sound like a freezing of the pitot tube because speed normally drops to zero when its frozen over, so it shouldn't fluctuate. Sometimes wind shear / turbulence and any microbursts can cause airspeed fluctuations but I doubt that they'd be that drastic unless weather was appalling.

As for the altimeter, it could be the same with the static port but again, it is very rare to impossible to happen so it sounds like something that would only occur in FS Dont Know

Pro Member First Officer
PH First Officer

Was not trying to be clever but rather than say no this is the answer thought it would be good to get people thinking....which it did! Anyway I completely embarrassed myself recently while doing my FI course the instructor said right I want you to brief me on the Pitot static system.....I did it very badly! Good job Jo!

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