Blocked static port / TCAS

[JeroenC]

Was doing unreliable airspeed in the sim. If it would be due static port blockage, what altitude would be passed to ATC via the txpdr, and what altitude does TCAS use?
Consider the memory items to set 4/10 degrees and 75/80%N1, this leads to blasting through all levels in eg busy london. If TCAS also doesnt work...

[NSEU]

Aircraft type?

e.g. on the 747-400, the TCAS gets its altitude data via the selected ATC transponder. The Left ATC transponder gets its altitude from the ADC selected on the Captain's instrument source select switch. The Right ATC transponder gets its ADC data from the ADC selected on the F/O's instrument source select switch.

[ASRAAM]

A320
The ATC transponder is capable of enhanced surveillance: It transmits the following parameters upon ground request:
Indicated airspeed, Mach number, and baro vertical speed, that are all supplied by the ADRs.
Magnetic heading, roll angle, ground speed, track angle, track angle rate, and inertial vertical speed, that are all supplied by the IRs.
Selected altitude and barometric reference settings supplied by the FCUs.
In the case of an ADR (1 or 2) failure, ADR 3 replaces the faulty ADR, when the AIR DATA SWITCHING Selector is set to CAP on 3 or F/O on 3.
IR/FCU parameters are only transmitted to:
ATC 1 by IR 1/FCU 1
ATC 2 by IR 2/FCU 2

[de facto]

These 2 pitch and thrust memory settings are for pilots who shouldnt be where they are seating....
I know what pitch and thrust ill use in case of unreliable airspeed and it damn wont be those..

[JeroenC]

Sorry, forgot to mention, B738.
On the 747 and 320 examples, what happens with TCAS with altitude input failure? CL does not mention transponder select switches.

[de facto]

Not sure why you are mixing unreliable airspeeds and static port blockage..
Your DU altitude info comes from pitot probes while your standby airspeed info comes from the stby pitot probe....nothing to do with static ports.
TCAS uses the barometric altitude information reported from your aircraft transponder,same ATC is receiving.(transponder 1:ADIRU1,transponder2:ADIRU2).
Maybe you should go the the ALT disageee nnc ....

[NSEU]

Your DU altitude info comes from pitot probes while your standby airspeed info comes from the stby pitot probe....nothing to do with static ports.

As far as I know, airspeed has always been computed using pitot AND static (not sure about the 787). These are basic principles.

According to my NG Maintenance Training notes, the "barometic altitude comes from the left or right ADIRU from the active ATC".
Both the left and the right ADIRUs feed each ATC transponder. The Altitude Source Switch on your control panel controls the which ADIRU feeds the active ATC transponder. There is no mention of automatic switching.

Basically, on the NG, the TCAS uses the altitude source you select on the ATC panel.

[Bobermo]

De facto, nice to see you know it better than Boeing! Setting a different value will surely keep your pm in the loop

[JeroenC]

Thanks for the replies.
Do the pitot probes on the NG automatically subtract static pressure? I was tought that speed = dynamic (=pitot) minus static pressure.

Now we have established that TCAS uses the selected baro altitude, how would u handle the described scenario? Defacto mentions ignoring Boeing guidance, my reasoning is that he is ( in this scenario) right/safer/airmanship etc.

[de facto]

Bobermo,
PM wil be notified obviously of my actions and reasons just as it was before this checklist arrived.
Not only for t/o should pilots know their pitch/thrust settings..its a basic thing,no?,You are now flying at FL 410 and pitots freeze...you have just got into ice crystals without noticing it...your standard pitch as you know is 2.5 ish degrees and thrust of 90%...well at least it was for the last hour or so..
Now you set set 4 degrees and 75 perc and see how it goes,nice way to add another cheese hole rolleyes:

[NSEU]

Do the pitot probes on the NG automatically subtract static pressure?

How can it automatically subtract static pressure if it hasn't got the value?

I was taught that speed = dynamic (=pitot) minus static pressure.

You are correct.

I was answering your question (as it was asked). I think the other folks were trying to tell you not to think about these things when you do have this kind of problem.

[MrSnuggles]

JeroenC

Depending on what aircraft in the sim, you could check out the Aeroperu 603 accident. Static port blockage caused erroneous altitude and airspeeds. Altitude was sent to ATC via transponder - ATC believed the aircraft was well above terrain but the aircraft crashed into the ocean a while later.

If I remember correctly this was a B757 or B767. Wikipedia has more information, I'm sure.