100 kt in RTO for Airbus

[b_737]

Hey guys,

Although I`ve been following the pprune for several years, this is my firs thread.

Anyways, during T/O, there is a callout of 100 knots for Airbus aircrafts. As you guys know there are some reasons for making that, which I`m interesting in determining speed discrepancy part of it.

My question : Is there any limit of the discrepancy between both IAS`s and if yes how much / from which document i can find it.

thanks in advance..

[Romasik]

I don't think there is a limit. Sometimes PM gets distracted and simply misses it out. Then what?

[Dash8driver1312]

On the Q400, we call at 80kts, the guidance is basically "any significant difference," and also as a check that the other guy is still awake. If there's no response, it is then a rejected take-off.

And yes, we are kind and give a second prompt at 90 just in case ;-)

[I-2021]

My question : Is there any limit of the discrepancy between both IAS`s and if yes how much / from which document i can find it.

Hi b 737,

You can find flight instrument tolerances for Airbus FBW in FCOM PRO-SUP-34. For your scenario the maximum difference between ADR 1 and 2 on PFDs is 6 kt.
Conditions to reject a takeoff below/above 100 kt are detailed in FCOM PRO-ABN-10. One of the conditions to reject above 100 kt is "Malfunctions or conditions that give unambiguous indications that the aircraft will not fly safely". That is left to your judjement. A speed discrepancy of a few knots is not easy to spot on takeoff and it does not necessarily mean that the airplane will not fly safely. A major speed discrepancy will become indeed a major issue.

Cheers.

[b_737]

thanks I-2021,
this is what i was looking for.

cheers.

[revertedrubber]

The 100kt call is made to assist in decision making process.

The take off is divided into low and high speed regimes, with 100kts being chosen as the dividing line. The speed of 100kts is not critical but was chosen in order to help the captain make the decision and to avoid unnecessary stops from high speed.

[safetypee]

Most modern instrument systems / ADCs incorporate a cross-comparator system which can be used to trigger a system caution; this may be inhibited as speed increases during takeoff. The aircraft technical description or ops manual should have details of this.
Airbus aircraft generally use a selective alert inhibit during takeoff (80kts?).
Their views on 100kts re speed crosscheck and safety are reflected in:-

http://www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-TOFF_DEP-SEQ04.pdf

[Capt Claret]

I don't think there is a limit. Sometimes PM gets distracted and simply misses it out. Then what?

Don't call 100 kt (in this example) if you've forgotten. Call the speed you're passing.

[nitpicker330]

Then what?? The PF calls it out and looks for a reply indicating the PM hasn't died on him......( it's not just a/c equipment failures the call is for :ok: )

If the PM remembers at 110 kts then he should ( as Claret says above ) call 110 kts...

If they both omit the call then hopefully one will be alive to rotate!! :eek:

[AirbusVince]

100 knot:

significant speed difference would indicate a possible of unreliable airspeed indication might be encountered.

it also making sure that the other guy is in the same page and following you on take-off to do his/her instrument checks flow

also a very good reminder that leaving 100 knots will be considered hazard to make an abort decision

When the captain hear this call out he will be go minded and prepare for anything that might happens. Because during take-off everything is done pretty fast, and captain has to act, expect and decide accordingly to any malfunction in a very short period of time.

we should consider very well to abort after 100 knots, if there will be any ecam warnings, because most of insignificant warnings will be inhibited during take-off phase from 80 knots till 1500

[CS-CCO]

Also worth mentioning that at 100kt you get the winds displayed in the PFD so a reminder to the PNF to check that and inform if there's a tailwind.

I've recently learned the importance of this from the jump seat as ATC is sometimes reluctant in changing runways at some Brazilian airports. Went pasted the 100kts and suddenly we saw 10-15kts tailwind which on a 28ºC AT and a heavy-ish A340 meant TOGA was needed.

I later learned that others knowing this ATC "habit" base the performance calculations on tailwind no matter what the weatherman says.

[Fly3]

I think you will find that the wind is indicated on the ND not the PFD.

[Natstrackalpha]

I Thought the 100kt call was to raise the cross onto the horizon bar (as you have been rolling with half scale down deflection to help keep the nose down) at 100 bring it up to the bar, at V1, know you will be flying soon, at Vr rotate.

also a very good reminder that leaving 100 knots will be considered hazard to make an abort decision

You are before V1 at 100 very often . . . - that is what V1 is for - you must STOP if somebody calls "Stop" at 102kts . . you will have enough runway - as you have just spent at least ten minutes doing pre-flight checks and the like, so as you can calculate exactly when you can/should call V1 "by".

That is why V1 is there - in order to save you from any damage.

If it is hazardous before V1 then your V1 speed is wrong.

[halfofrho]

I Thought the 100kt call was to raise the cross onto the horizon bar (as you have been rolling with half scale down deflection to help keep the nose down) at 100 bring it up to the bar, at V1, know you will be flying soon, at Vr rotate.

This is not what the 100kt call is for. The forward pressure should be gradually released at 80kts so its back at neutral by 100kts.

As previously mentioned, the 100kt call is to make sure that you both have a good speed read out, that the other person is still awake, and to aid in the decision making process between the low and high speed regime during the take-off roll ("Before 100kts we will consider stopping for any malfunction.").

[Natstrackalpha]

("Before 100kts we will consider stopping for any malfunction.").

My/our version is Before V1 either of us can call stop for . . . .?

Also, though, in the L1011-1 the call was 80kts, "80kts check" so yes, I agree to what you are saying and that is the reason for the 100kt call, the only difference here is that we do the 100 kt call like you all, but the briefing above is different. In that we are planning to stop anytime before V1 and planning to fly anytime after V1.

Personally, after V1, please give me the sky!

Having said that, a dual engine failure after V1 could really spoil your morning. EFATO? most certainly would be the trees or the runway end especially without the luxury of 2REV - on second thoughts, I would sooner have a very, very long runway.

[nitpicker330]

From the Airbus FCTM------

To assist in the decision making process, the take-off is divided into low and high speed regimes, with 100 kt being chosen as the dividing line. The speed of 100 kt is not critical, but was chosen in order to help the Captain make the decision and to avoid unnecessary stops from high speed. Below 100 kt, the Captain should seriously consider discontinuing the take-off if any ECAM warning is activated. Above 100 kt and approaching V1, the Captain should be "go-minded" and only reject the take-off in the event of a major failure such as a fire warning or severe damage, sudden loss of thrust, any indication that the aircraft will not fly safely, or if an ECAM warning occurs.

Examples of ECAM warnings that may occur are ENG or APU FIRE, ENG FAIL, ENG OIL LO PR, CONFIG, SIDESTICK FAULT, REVERSER UNLOCKED, and L+R ELEV FAULT. If a tyre fails within 20 kt of V1, unless debris from the tyre has caused noticeable engine parameter fluctuations, it is advisable to get airborne, reduce the fuel load and land with a full runway length available.

V1 is the maximum speed during the take-off roll at which the pilot must take the first action to stop the aircraft within the accelerate-stop distance. For certification purposes, an engine failure recognition time of 1 second is allowed between the engine failure and V1. Additionally a distance margin, equivalent to 2 seconds at a constant speed equal to V1, is added to the accelerate-stop distance.This increases the safety margin.

V1 is also the minimum speed in the take-off roll, following a failure of the critical engine at V1, at which the pilot can continue the take-off and achieve the required height above the take-off surface within the take-off distance.The RTO Operational Margins diagrams below, give an indication of the consequences of rejecting the take-off after V1 and/or using improper procedures.

The decision to reject the take-off is the responsibility of the Captain and must be made prior to V1. If a malfunction occurs before V1, for which the Captain does not intend to reject the take-off, he announces his intention by calling "GO". If the Captain decides to reject the take-off, he calls "STOP". This call both confirms the decision to reject the take-off and also indicates that the Captain now has control.This is the only time that hand-over of control is not accompanied by the phrase "I have control"

[Linktrained]

RTO at 80 kts and then...

The Brittannia returned to apron at KIN. Steps rolled up to inspect Pitot tubes. All appeared normal but effectively dead. F/E was unable to find fault. Engineer was requested from base in UK. ( Telex was available, then.)

He arrived and fixed our problem.

The Catering had gone bad in the heat, and now we had NO Catering for 130 + passengers... And it was a Bank Holiday in KIN. Requested a Diplomatic Overflight Clearance from Cuba. Flew to Toronto where we had a Base and could get Catering QUICKLY. Flew back to UK using my discretion with my double crew, arriving only a couple of days late. My Chief Pilot had thought that I had taken everyone on a sightseeing tour. ( What a reputation to have !)

Thanks to PPRUNE some decades later, I saw that Birgenair had had Black and Yellow Mud Dauber Wasps in their Pitot tubes, which caused their accident. I assume that this is what had caused my problem. ( My Pitot head covers had appeared a bit worn and were snagged on return to base.)

NOW I know what may have happened. Mobiles etc. did not exist. As a Captain I was expected to do what ever was necessary for the orderly and safe conduct of the flight, even if a little late !

[Natstrackalpha]

nitpicker 330

`sweet`:ok:

[nitpicker330]

The A330 FCOM 3 supplementary procedures section also details maximum discrepancies between ADR 1 and 2 ( plus other combinations ) for IAS MACH indications on the PFD's

It shows that for a ground check it is 6 kts / .008 Mach maximum allowed difference.

Therefore you could say that at 100kts if the PFD IAS displays differ by more than 6 kts then you should "Stop" whether or not the Captain decides to about is up to him.

I know of one incident where the crew detected an error greater than allowed and they stopped.:ok: