TAT probe
TAT probe
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Cheers Qavion,
The story behind this is that we lost TAT probe heat on take-off and our QRH just said "flight in icing conditions may result in some erroneous flight instrument indications"
We also lost Autothrottle, and I wonderd how the two relate.
So we DO need it!!
411A,
Would this also affect the autothrottles evaluation of thrust required due to the OAT not being available?
Our manuals are cr@p!!!
[This message has been edited by Jonty (edited 17 February 2001).]
The story behind this is that we lost TAT probe heat on take-off and our QRH just said "flight in icing conditions may result in some erroneous flight instrument indications"
We also lost Autothrottle, and I wonderd how the two relate.
So we DO need it!!
411A,
Would this also affect the autothrottles evaluation of thrust required due to the OAT not being available?
Our manuals are cr@p!!!
[This message has been edited by Jonty (edited 17 February 2001).]
Guest
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"Our manuals are cr@p!!!"
I know the feeling!
According to my 747-400 notes, when the aircaft is operating in VNAV Speed mode, the A/T computer (which is contained within the Flight Management Computer on a 747-400), calculates a desired TAS value and compares this with the current aircraft "airspeed" to generate a difference value. This difference value drives the throttle levers. I know TAS is fed to the FMC from the DADC's (probably along with lots of other things), but I can't state unequivically that the "current aircraft airspeed" in my text is _TAS_, but this would make sense. So I can see how TAS might affect A/T engagement in at least one A/T mode.
Does your 757 have digital engine control (FADEC)? If the EEC's are using TAT data provided by the TAT probe(s) mounted on the airplane nose, this may also be a factor in A/T disengagement.
Anyway....Hope this helps.
Cheers.
Q.
I know the feeling!
According to my 747-400 notes, when the aircaft is operating in VNAV Speed mode, the A/T computer (which is contained within the Flight Management Computer on a 747-400), calculates a desired TAS value and compares this with the current aircraft "airspeed" to generate a difference value. This difference value drives the throttle levers. I know TAS is fed to the FMC from the DADC's (probably along with lots of other things), but I can't state unequivically that the "current aircraft airspeed" in my text is _TAS_, but this would make sense. So I can see how TAS might affect A/T engagement in at least one A/T mode.
Does your 757 have digital engine control (FADEC)? If the EEC's are using TAT data provided by the TAT probe(s) mounted on the airplane nose, this may also be a factor in A/T disengagement.
Anyway....Hope this helps.
Cheers.
Q.
Guest
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For 757 ,
when the TAT heater is inoperative on single TAT aircraft, the TMC considers temperature from the TAT to be invalid and disconnects the autothrottle. On dual TAT aircraft, airplane systems use the unaffected TAT signal when reconfigured to use Center Air Data.
With an inoperative Thrust Management Computer, the Autothrottle System will be inoperative and
the following displays on EICAS will be affected:
1. EGT (and N1, N2, N3 for RR engines) amber indications which are normally inhibited during takeoff or go-around will not be inhibited,
2. Reference EPR will not be available,
3. Assumed temperature (if used) will not be available,
4. Thrust reference mode (TO, CLB, etc.) will not be available.
5. Airplanes that do not have speed tape: the SPD flag may remain in view on the EADI.
With reference FADEC engines, if TAT probe heat fails EEC wiil receive an TAT invalid signal and default to using its own temp sensor ( aircraft data being preference .)
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Fools rush in where Angels fear to tread
when the TAT heater is inoperative on single TAT aircraft, the TMC considers temperature from the TAT to be invalid and disconnects the autothrottle. On dual TAT aircraft, airplane systems use the unaffected TAT signal when reconfigured to use Center Air Data.
With an inoperative Thrust Management Computer, the Autothrottle System will be inoperative and
the following displays on EICAS will be affected:
1. EGT (and N1, N2, N3 for RR engines) amber indications which are normally inhibited during takeoff or go-around will not be inhibited,
2. Reference EPR will not be available,
3. Assumed temperature (if used) will not be available,
4. Thrust reference mode (TO, CLB, etc.) will not be available.
5. Airplanes that do not have speed tape: the SPD flag may remain in view on the EADI.
With reference FADEC engines, if TAT probe heat fails EEC wiil receive an TAT invalid signal and default to using its own temp sensor ( aircraft data being preference .)
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Fools rush in where Angels fear to tread
Guest
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Feret, that was the exact same problem we had.
Golden Rivet,
where were you when we needed you?!!! And why couldnt the QRH say somthing along those lines.
Just one question? our aircraft have two TAT sensors but within the same housing (on the right side of the aircraft, next to two doors that nobody seems to know about). If this housing lost its heat, I would assume that both TAT sensors would be U/S and selecting centre air data would have no effect. Is this true? also if you can shed any light on what the two doors do (right hand side, fwd of the fwd cargo door) it would be appreciated
Cheers!!
Golden Rivet,
where were you when we needed you?!!! And why couldnt the QRH say somthing along those lines.
Just one question? our aircraft have two TAT sensors but within the same housing (on the right side of the aircraft, next to two doors that nobody seems to know about). If this housing lost its heat, I would assume that both TAT sensors would be U/S and selecting centre air data would have no effect. Is this true? also if you can shed any light on what the two doors do (right hand side, fwd of the fwd cargo door) it would be appreciated
Cheers!!
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Jonty
Which aircraft are we talking about ? 757 I assume.
The two mysterious doors on the r/h side of the nose are the negative pressure relief valves which prevent cabin pressure from becoming less than ambient in the event of an emergency decent ( perish the thought ! )
The negative relief doors are spring loaded closed and open on the negative cabin pressure of - 0.75 psi thereby preventing the airframe squishing itself.
As for the dual TAT ? I think I'll have to do a bit of research on that one !
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Fools rush in where Angels fear to tread
[This message has been edited by Golden Rivet (edited 03 March 2001).]
Which aircraft are we talking about ? 757 I assume.
The two mysterious doors on the r/h side of the nose are the negative pressure relief valves which prevent cabin pressure from becoming less than ambient in the event of an emergency decent ( perish the thought ! )
The negative relief doors are spring loaded closed and open on the negative cabin pressure of - 0.75 psi thereby preventing the airframe squishing itself.
As for the dual TAT ? I think I'll have to do a bit of research on that one !
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Fools rush in where Angels fear to tread
[This message has been edited by Golden Rivet (edited 03 March 2001).]
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Double TAT probe( L/H & R/H of Nose )only to be found on 757-300 which is fitted with 3 ADIRU's ( combination of ADC & IRU in same box )instead of 2 ADC's and 3 IRU's.
Bog standard 757-200 TAT probe fitted with twin sensing elements and one heating element( R/H side of nose fwd of those mysterious doors ! )Loosing the heater element will cause both TAT sensing element signals to become invalid to certain systems.
If you think that loosing the TAT heater causes you problems, you should see what happens on the A320 if you lose the captains clock !!!
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Fools rush in where Angels fear to tread
Bog standard 757-200 TAT probe fitted with twin sensing elements and one heating element( R/H side of nose fwd of those mysterious doors ! )Loosing the heater element will cause both TAT sensing element signals to become invalid to certain systems.
If you think that loosing the TAT heater causes you problems, you should see what happens on the A320 if you lose the captains clock !!!
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Fools rush in where Angels fear to tread
Guest
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Surely your winding me up now !
What do they teach pilots these days about the airplanes they are flying ? Please tell me your not a Captain !!
The two pressure relief doors aft of the left hand wing root fairing are POSITIVE pressure relief doors as opposed to the NEGATIVE relief doors at the front.
Positive pressure relief valves prevent differential pressure from exceeding stuctural limits in the event of a pressurisation system malfunction. The valves have a primary metering section limiting positive pressure to 8.95 psi diff and a secondary metering section as a back-up which operates at 9.42 psi diff.
These valves should be inspected each preflight and if opened a flag is visible.
(not uncommon so keep your eyes open when doing your walk-around )
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Fools rush in where Angels fear to tread
What do they teach pilots these days about the airplanes they are flying ? Please tell me your not a Captain !!
The two pressure relief doors aft of the left hand wing root fairing are POSITIVE pressure relief doors as opposed to the NEGATIVE relief doors at the front.
Positive pressure relief valves prevent differential pressure from exceeding stuctural limits in the event of a pressurisation system malfunction. The valves have a primary metering section limiting positive pressure to 8.95 psi diff and a secondary metering section as a back-up which operates at 9.42 psi diff.
These valves should be inspected each preflight and if opened a flag is visible.
(not uncommon so keep your eyes open when doing your walk-around )
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Fools rush in where Angels fear to tread
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I can tell you what they teach us on a conversion course, FU@K ALL!!!!
Our manuals dont mention the doors at all, It talks about the pressure relief system stating the pressures you have said, but nothing about doors.
It also says nothing about a dry bay in the wings or the drain holes inboard of the engines.
What they give us is the MEL a mobile phone and the number of maintroll to phone if we see somthing we dont like.
I think the attitude is the enginers will tell you if its serviceable so you (the pilots) dont need to know about it, God bless the JAA
Thanks for the info GR.
PS asked meny people about the doors and no one knew about them (Pilots that is)
Our manuals dont mention the doors at all, It talks about the pressure relief system stating the pressures you have said, but nothing about doors.
It also says nothing about a dry bay in the wings or the drain holes inboard of the engines.
What they give us is the MEL a mobile phone and the number of maintroll to phone if we see somthing we dont like.
I think the attitude is the enginers will tell you if its serviceable so you (the pilots) dont need to know about it, God bless the JAA
Thanks for the info GR.
PS asked meny people about the doors and no one knew about them (Pilots that is)
