777-300ER Engine anti-ice

[767-300ER]

We use ACARS performance data and in the take-off WAT, we specify if there's visible moisture...the WAT utilizes the latest METAR for met data.
At times when OAT is about 8 or 9º and there is visible moisture, we are required to use Eng Anti-Ice. After start we turn on the Eng Anti-Ice. Sometimes we get a ENG ANTI-ICE EICAS message. Checking the TAT it shows 11º...the EICAS procedure has us turn off the Eng Anti-ice.

Clearly the EICAS system uses the TAT to make the decision to post the EICAS message, but the ACARS WAT is using the METAR value of OAT.

What would be the prefered option? Leave Eng Anti-ice on and cancel the EICAS message or turn off the Eng Anti-ice??

[tdracer]

Just my opinion, but having Engine Anti-Ice on at +11 C doesn't hurt anything (different matter if it's +40 C) - just a little fuel burn. Far better to have EAI ON and not need it than to have it OFF and need it...
I've seen firsthand the damage that an inlet ice shed can do - it wasn't pretty.

[awair]

Check the AFM:

TAT in the air,
OAT on the ground…

… or has the AFM been removed from the aircraft?

[FullWings]

Checking the TAT it shows 11º...the EICAS procedure has us turn off the Eng Anti-ice.
It will even bring that checklist up at 10C.

Personally, I run with SOPs unless I have good reason not to. Getting in the habit of ignoring checklists is a bit of a slippery slope on the way towards normalisation of deviance, despite the fact that in this case it doesn’t really matter (you can go with the EAI valve deactivated open up to 38C ambient). The question is, would you do this on a line check? Are you happy with inventing a new datum of 11C for putting the EAI on, or maybe that should be 15C, just to be on the safe side, despite Boeing’s instructions?

As long as you turn it on if ground icing conditions exist, like you have to do after landing, then it’s not a problem.

[Check Airman]

The airplane and metar sensors are showing different temperatures, right on the threshold.



At that point, I’d say it’s a judgement call. Look at the conditions and make a decision on what’s actually going on. Is it 11 degrees and overcast at 300ft? Is it 10 degrees with a clean runway and no low clouds?



Not everything can be cut and dried. SOP can’t be invented for every conceivable situation. If I wanted to do one thing, and the other guy felt more comfortable doing the other, I’d just go with it and not lose any sleep. By the time the after takeoff checklist is complete, it’ll be a moot point and quickly fading from memory anyway.

[BraceBrace]

So METAR measured at a certain time point in the history somewhere around the airport is more reliable than the actual measurement of temperature at the exact time, at the exact location where the engines are?

Go with what the aircraft says. The performance calculations cover you when you would eventually end up using engine anti-ice, based on what the aircraft is telling you.

Turn it the other way around. If METAR says 11°C, and temperatures drop 1°C... you're not going to use engine anti-ice because METAR says so?

(ps: TAT on the ground is same as SAT as long as airspeed is 0)

[Vessbot]

So METAR measured at a certain time point in the history somewhere around the airport is more reliable than the actual measurement of temperature at the exact time, at the exact location where the engines are?


Maybe. I fly a different aircraft, where the manual says specifically not to use the aircraft-measured temperature on the ground.

[tdracer]

Maybe. I fly a different aircraft, where the manual says specifically not to use the aircraft-measured temperature on the ground.
Depends on the aircraft. TAT sensors are heated to prevent them from icing up in flight (getting that heat right - so that it keeps the probe warm enough to prevent ice forming without adversely affecting the temperature measurement - is a very non-trivial engineering challenge). Some aircraft have TAT probes that are 'aspirated' - air is blown around the probe while on-ground to prevent the probe heat from affecting the TAT measurement statically - but not all aircraft have that feature. IF the TAT probes are not aspirated, on-ground TAT is not considered valid.
The 777 (and all current production Boeings) have aspirated TAT probes that should remain accurate on-ground. Note that there are 'latent' malfunctions that can adversely affect the TAT probe aspiration - debris in the probe being a big one.

[BraceBrace]

Maybe. I fly a different aircraft, where the manual says specifically not to use the aircraft-measured temperature on the ground.

The question is about the 777.

It's pretty visible in the temp indication on the ground when your 737 is equiped with unaspirated TAT probes.

[Zar_1]

Just a question, kinda off-topic... but in the 73, in an airline with a fleet having both aspi/non-aspi TAT probes how would one know which particular one is fitted to the A/C. As in, how do y'all practically handle small differences bet. different MSN's.

[8che]

So METAR measured at a certain time point in the history somewhere around the airport is more reliable than the actual measurement of temperature at the exact time, at the exact location where the engines are?

Go with what the aircraft says. The performance calculations cover you when you would eventually end up using engine anti-ice, based on what the aircraft is telling you.

Turn it the other way around. If METAR says 11°C, and temperatures drop 1°C... you're not going to use engine anti-ice because METAR says so?

(ps: TAT on the ground is same as SAT as long as airspeed is 0)

Geez...where do we start with all this rubbish ?

No.... you don't go with the aircraft. on the ground you go with the ATIS (not metar ) or ATC reported weather for the airport. That's the official legally reported weather for that airfield, By your logic why go with the weather report at all when at the holding point we can trust the aircraft to say there is never any wind for take off !
In most cases the temperature sensed by the aircraft is normally greater than the ATIS which also following your logic means we would be turning the anti ice off in icing conditions.

The B777 FCOM supplementary procedures / AFM and Boeing's icing conditions definition clearly state that TAT is only to be used in the air and OAT is used on the ground. Whether knowing the TAT is aspirated or not is irrelevant. The TAT probe is the only probe not heated on the ground so it is unreliable until airborne.

If you meet Boeing's definition of icing conditions with the ATC/ATIS reported OAT of 10 degrees or less then you are in icing conditions and the engine anti-ice needs to go ON whatever the aircraft TAT sensor may say. If the EICAS ANTI-ICE ON message then appears while taxing by all means discuss and checklist override the ECL but leave the Engine Anti-ice ON. Once airborne TAT takes over and the aircraft rules over the ATIS.

No one is suggesting the ECL is ignored but the ECL is designed as a tool to assist crews in decision making not make decisions for them. It has limitations and was never designed to be blindly followed to replace crew Competency/Airmanship.

[FlightDetent]

Turn it the other way around. If METAR says 11°C, and temperatures drop 1°C... you're not going to use engine anti-ice because METAR says so? No. If it dropped another one to 9° C I would because the AFM and my boss say so if there was visible moisture with VIS <1600m or precipitation.

Something to do with airflow over the inlet lip, namely at the rated take-off air-guzzling thrust and the subsequent drop of local temperature where heating is so kindly installed. Guess we must have paid for that....

[safetypee]

Not so long ago https://en.wikipedia.org/wiki/Carburetor_icing

The same / similar issue; Engine intake (Carburettor) icing is caused by the temperature drop in the intake, - 'a Venturi'. …If the temperature drops below freezing, water vapour will freeze onto … internal surfaces of … the engine / intake.

https://skybrary.aero/articles/ice-formation-aircraft
,

[BraceBrace]

No. If it dropped another one to 9° C I would because the AFM and my boss say so if there was visible moisture with VIS <1600m or precipitation.

Of course you need visible moisture and vis < 1600m.

But the phrase in the books is 10°C or below. Not below 10°C. Now we need the quote from those same 777 manuals stating SAT calculation is unreliable on the ground. I haven't found it, but feel free to correct me if I'm wrong.

[8che]

There seems a lot you haven't found. Did you not notice the part that explicitly states only OAT not TAT (or SAT) is to be used for determining icing conditions on the ground. Its in the FCOM and AFM which forms part of the certification of the aeroplane.

Does the FCOM or AFM allow use of the EICAS Engine Anti Ice On message to turn the protections off on the ground ? Absolutely not , it states:Use the temperature and

visible moisture criteria because late activation of

engine anti-ice may allow excessive ingestion of ice

and result in engine damage or failure.

Guess where the EICAS Engine Anti Ice On message comes from ? The TAT probe (or SAT probe if you want to call it that).

There are actually 3 TAT probes on the 777 that are used for engine take off thrust calculations but that process is complicated and certainly not part of crew icing diagnosis.

Are you aware of all the regulations on how airfield temperature has to be scientifically produced to be officially reported ? Perhaps a visit back to the books to look at Stevenson Screens and some ATPL bits is needed.

[Zar_1]

Guys, I'm not a pilot (yet), and thus I may be totally wrong...

But if it's only a matter of 1 or 2 degrees Celsius, why not use the Anti-Ice (and take the minor, associated performance penalty), than to risk not using it. AFAIK, the 773 isn't exactly underpowered, so in most cases it wouldn't lead to an issue.

[BraceBrace]

There seems a lot you haven't found. Did you not notice the part that explicitly states only OAT not TAT (or SAT) is to be used for determining icing conditions on the ground. Its in the FCOM and AFM which forms part of the certification of the aeroplane.

And what is OAT? And what is TAT?

The phrase you are referring to is a phrase you will find in any Boeing commercial jet manual. You don't have to turn around the phrase and create limitations out of it. The reason why the phrase is written down like this in any manual is to point out that INFLIGHT you have to use a much more SPECIFIC tool: TAT, which is an exact indication on the flightdeck. ON THE GROUND, you use OAT. I tend to feel some people think OAT is a term relating ONLY to METAR temperature. If you would read the books even more detailed, you would notice that in performance manuals Boeing sometimes refers to Airport OAT - not OAT - to make a distinction. There is also referred to reported OAT. And actual OAT.

SInce you like to refer to books. I don't find Boeing anywhere specifying the OAT mentioned is METAR temperature. The term OAT is mentioned in their books multiple times on all fleets:

B737 classic/NG: in the FCOMs the difference between aspirated and unaspirated probes is explained, as well as the effect of the use of pitot heat and packs. I think there are also FCOM's that explicitely state indicated TAT on the ground is not to be used as an indication of OAT.

B744: FCOM states "TAT indication on the ground approximates OAT. TAT probe must be aspirated by bleed air".

B777: FCOM explains TAT is a calculated value by ADIRU and SAARU. It uses temperature probes and calculates. Take your FMC and look at page thrust limit page, top line. What does it say? Does it say OAT or does it say TAT? Where do these values come from? And my question remains: show me the line in the books about temperature calculations being unreliable on the ground. I'll admit 777 has been 7 years, I don't mind being told I missed certain points.


BTW: you do the same thing inflight with your crewmembers - telling them to go study the books because you are right above all?

[FullWings]

That’s all very interesting, but the actual question was related to the fact that when the aeroplane sees a temperature of above 10C, the EAI selector is ON and there is no ice detected, it will bring up a checklist asking for you to turn it to AUTO or OFF. Should you ignore this checklist?

My answer is that unless you feel the measurement is significantly in error (and that’s going to cause other problems), then it is SOP to action the checklist in the way that the manufacturer intended, otherwise they would not have made it pop up in the first place. If you choose to ignore the [ ] ANTI-ICE ON when it appears, what new threshold are you going to use to determine whether it should be on or not, as you’re going to need one if you don’t trust the aeroplane?

[ScepticalOptomist]

What would be the prefered option? Leave Eng Anti-ice on and cancel the EICAS message or turn off the Eng Anti-ice??

Just follow the SOP. Annoying I guess, but it keeps the framework of EICAS / Checklist use in tact.

Ignoring the checklist is a slippery slope..

[8che]

Guys please, no one is suggesting a non-normal check list is ignored.

With any Boeing non-normal checklist a “condition statement” and/or objective statement is first stated. It is crucial that crews read this condition statement and understand it before deciding on whether to action the rest of the check list. So many crews dive in and gloss over the condition statement.

ANTI-ICE ON

Condition : All of these occur:

1) An anti-ice selector is on
2) TAT is more than 10 degrees C
3) Ice is not detected.

This message is not relevant (on the ground) if the officially reported ATIS indicates icing conditions. TAT is not part of ground assessment. Ice detection is not enabled on the ground. This checklist is not relevant until airborne because Boeing clearly states that to make a decision on Engine anti ice selection on the ground, you must rely solely on the OAT temperature and visible moisture criteria which can only come from an approved aerodrome source. Boeings definition of icing conditions is in black and white.

What you are saying is that when in icing conditions as defined by Boeing, you will turn the engine ice protection off because the aircraft told you to ?

It has never been SOP to blindly follow a checklist. Boeing clearly state there are limitations with checklist creation and it’s use. Boeing state “ Flight crew must be aware that checklists cannot be created for all conceivable situations and are not intended to replace good judgement. In some situations, at the Captains discretion, deviation from a checklist may be needed”.

Any command course worth the name or good type rating course will demonstrate a number of scenarios where blindly following a non-normal checklist will take you down a rabbit hole to an aircraft undesired state.

The ECL was never designed to replace good crew judgment and decision making. Our industry tries to build crew competencies leading to the build up of crew resilience. Simply saying we must always follow a checklist is rather depressingly a demonstration to the contrary.

[ScepticalOptomist]

What you are saying is that when in icing conditions as defined by Boeing, you will turn the engine ice protection off because the aircraft told you to ?
.

No,they are saying the opposite, safer option - leave the anti ice ON, even when clearly in clear air.

[BraceBrace]

This message is not relevant (on the ground) if the officially reported ATIS indicates icing conditions. TAT is not part of ground assessment. Ice detection is not enabled on the ground. This checklist is not relevant until airborne...

Can you please for once show where your information comes from?

The Boeing statement is to use OAT, Boeing does not anywhere say TAT cannot be used on the ground. OAT gives you more freedom, there is nowhere any requirement stated that OAT is ONLY metar reported temperature. If you decide to switch if to AUTO, fine. If you decide to keep it ON, fine, but be aware you are overruling a checklist in theory you are required to follow. I don't know any company that is going to hassle you for this decision. But don't come claiming this story about captaincy, common sense, blablabla... because you are not doing anything wrong by following the checklist. The Boeing statements on checklist creation are common for all fleets, however you abuse those statements. Boeing is not saying anywhere to "disregard" a checklist, Boeing does not say this checklist is not "relevant" in this situation.

"Common sense" is the most abused phrase in aviation by pilots, as is "we've been doing it like that for years". My request remains: show me where Boeing states B777 TAT is unreliable on the ground.

[tdracer]

My request remains: show me where Boeing states B777 TAT is unreliable on the ground.

Given that the FMC uses TAT to determine thrust set during TO, I sure hope TAT is not 'unreliable' on the ground...

[FullWings]

Also, 777 ECL checklists can inhibited or modified when the aircraft senses it is on the ground. Boeing appear to have chosen not to do this with the ANTI-ICE ON checklist; maybe this is an omission/error on their part, or maybe it’s deliberate?

As far as TAT and OAT goes, if you’re not moving very fast through the air, they are practically equivalent. Even at 100kts there is ~1C difference. If a system can measure TAT within acceptable tolerances (see above post) when at 0kts on the runway, then it can do it everywhere else on the ground and it is effectively OAT.