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New Takeoff performance with a change of air temperature

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New Takeoff performance with a change of air temperature

Old 5th Jan 2023, 04:38
  #61 (permalink)  
fdr
 
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Originally Posted by tdracer
Sorry, but that is not only wrong, it's dangerously wrong. If actual OAT is 25, and ATM comes up with 75 for thrust setting, that simply means that the thrust (typically N1) for 75 can still be used safely.
If the actual OAT goes up, the aircraft performance goes down (hotter air = less lift at the same airspeed). IF you don't redo your ATM calcualation for the new OAT, you're thrust setting will be too low for that OAT. Plus, if you're talking N1 thrust setting, 100% N1 at 50 degrees creates significantly less thrust than the same physical N1 at 25 (that old "square root theta" thing - thrust is constant at corrected N1, not physical N1).
The ATM that is applied is valid, so long as the actual temperature doesn't exceed the assumed temperature. The crew are finding the limit case for the weight they are at, therefore as far as runway performance goes, they are hot to trot. However.... the V speeds should be recalculated if a significant change occurs. At least one airline gets around that by using the V speeds for the limit case... can't say I really like that concept. The company flight ops engineering or performance team can conduct a sensitivity analysis and make a determination as to when they wish the V speeds to be corrected to match actual conditions or not.

...

As to concerns that a pilot may ask for guidance on the subject, I personally am comforted that they would do so. Having an uncertainty in what is necessary is a troubling situation to find yourself in. Performance is bad enough without having some means to get a better comprehension than an airline and national licensing system may achieve. I do performance flight testing in R&D, and I end up asking questions also...

Boeing's performance manual, the Performance Engineers Manual, or Jet Transport Performance methods, should be mandatory reading for anyone with a Part 25 rating... so should the USNTPS FTM-108 Fixed Wing Performance and FAA AC 25.7D, Flight Test Guide for Certification of Transport Category Airplanes. Airbus's performance is a dark art...


JTs comment is on point, having a cognitive awareness of the situation saves a lot of heartache, like the bingle of the B742F at Halifax NS. The more we go towards a computer solution, the greater the chance of a gross error leaving bits of tin around the end of the paddock. Having a conceptual understanding of what the numbers means will assist in recognition when things are not quite as expected. Recall, that to be airworthy, the aircraft must conform to its TCDS as a part of its requirement , and the other is that it must be safe to fly, whatever that may mean. The TCDS includes the basis of certification that includes the AFM which has the legal TO performance requirements. Much performance is guidance material only and not certified, but TO performance is not subject to negotiation.
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Old 6th Jan 2023, 04:24
  #62 (permalink)  
 
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On a different point.

My operator hasnít allowed us to update to iPadOs 16 yet. Are there other operators with this?
If so, anybody got any idea what the holdup is?

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Old 6th Jan 2023, 10:29
  #63 (permalink)  
 
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Originally Posted by dogtired
On a different point.

My operator hasnít allowed us to update to iPadOs 16 yet. Are there other operators with this?
If so, anybody got any idea what the holdup is?
Usually itís the authors / owners of the software suites that need to approve the upgrade. They arenít usually very fast.
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Old 6th Jan 2023, 18:55
  #64 (permalink)  
 
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Originally Posted by fdr
The more we go towards a computer solution, the greater the chance of a gross error leaving bits of tin around the end of the paddock.
Why? History has proven completely opposite is correct. We think we can do better. Usually we canít. Computers can be tested on the ground under pressure and they will handle complexity in a consistent way. Humans need simplicity, and even then won't survive under pressure.

Last edited by BraceBrace; 6th Jan 2023 at 19:12.
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Old 7th Jan 2023, 04:06
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Originally Posted by dogtired
On a different point.

My operator hasnít allowed us to update to iPadOs 16 yet. Are there other operators with this?
If so, anybody got any idea what the holdup is?
itís approved with my mob so not sure what the holdup is with yours.
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Old 7th Jan 2023, 07:24
  #66 (permalink)  
 
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I checked on EFB OAT 20 į flex56į. With change of OAT by 5į to 25į there was no difference in speeds nor flex. Change of QNH by 4hP didn't change them either.

Last edited by vilas; 7th Jan 2023 at 08:40.
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Old 7th Jan 2023, 09:32
  #67 (permalink)  
 
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iOS 16.1.1 was finally cleared for use in mid November. There were some holdups with compatibility.
You might have some other managed apps on there that are incompatible. .
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Old 9th Jan 2023, 13:08
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Originally Posted by WhatShortage
If I do that question to a captain while on line training that flight would've been a nightmare and probably a big redflag for not knowing tref trefmax etc...
Do you mean because of adding more OAT means nothing because you're assuming the maximum already?

As far as I am concerned and some have mentioned already, beyond a certain temperature flex will keep going down due to performance limitations and before that point it won't matter if it goes down.

There's no stupid question and certainly this is not.
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Old 19th Jan 2023, 09:22
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Change of temperature changes your performance. Always do another one, or do the initial performance anticipating this increase in temperature. Too little thrust is never good.
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Old 19th Jan 2023, 22:06
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Originally Posted by 737pilotguy
Change of temperature changes your performance. Always do another one, or do the initial performance anticipating this increase in temperature. Too little thrust is never good.
You might want to read the thread first.
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