View Full Version : B737, takeoff or return to the stand

22nd Mar 2010, 23:06
Hi guys,

I was talking with a friend of mine (a captain) about a possible ANTISKID INOP light illuminated during taxi or during pushback while starting the engines.

As you know, in these phases we are considered to be "inflight" so all the planning and dispatch procedures are no more applicable; thus, we have to do the NNC (non normal checklist) which doesn't tell anything about the takeoff, but refers only to landing performances (to check the advisory non-normal landing distances).

The question is: may you takeoff or not?

Don't mind about the situation, if it's a base airport or not etc (we will talk about it later). Just answer if you are legally allowed to takeoff and if you have to modify the takeoff performance calculations (remember, these are "dispatch" performances).


22nd Mar 2010, 23:37
Well, as you correctly stated the MEL is no longer binding, but should still serve as a reference... To my understanding it is legally possible to takeoff (unless something goes wrong and a clever attorney accuses the PIC of careless negligence for some reason). According to our MEL an airplane is dispatchable with the antiskid system inop as long as the procedures for flight with A/Skid inop are being adhered to (no reduced thrust takeoff, no takeoff from a wet or contaminated runway etc etc)... Would I do it? Probably not, I'd rather have a tech check it out.

22nd Mar 2010, 23:57
That's the point.

The question is, do you perform all the procedures indicated in the MEL (no Assumed temperature, no takeoff on wet or contaminated rwys, weight penalty and V1 adjustment) even if these are dispatch procedures?

Boeing states, in the NNC instructions in the QRH:

Non–normal checklists also assume:

• During engine start and before takeoff, the associated non–normal
checklist is done if a non-normal situation is identified. After completion
of the checklist, the Dispatch Deviations Guide or operator equivalent is
consulted to determine if Minimum Equipment List dispatch relief is

The bold font sentence is a bit misleading. "available" doesn't mean that it should be adhered to in that moment but it could mean that "you have that item in the MEL or DDG, so the airplane is considered able to fly"; that's the opinion of a couple of collegues.

That is what i want to better understand.

However, we know that the real conditions and environment are important to make a good decision. If i'm at my base airport going to an airport without technical assistance, I'd rather turn back to the stand and make the airplane dispatched with the antiskid inop.

23rd Mar 2010, 00:12
I'd like to explain better.

Some people say that the antiskid inoperative doesn't modify the "actual" (not factored) takeoff distances, so once we are in the "flight" phase (when the dispatch rules and procedures are no longer applicable) we don't have to apply corrections on our takeoff performances as this is a dispatch requirement only.

So, if you have an antiskid inop light during taxi, you are legally allowed to continue as long as you do the NNC.

Callsign Kilo
23rd Mar 2010, 00:42
With the basic philosophy of how the MEL, DDG and NNC works and when it should be applied, then sure you have met the 'legal' requirements and you can dispatch.

But as a commander you would consider the performance limitations at both departure and destination plus the environmental factors. That's basic airmanship regardless if you have performed the basic legal requirements of the NNC and dispatch guidelines.

We all know that if it came down to a Q&A session with your fleet manager or chief pilot, the factor of whether you performed the NNC adequately would not be his only concern

23rd Mar 2010, 00:52
I think it's called "airmanship".

I really believe that any captain who lined up for take off with the antiskid light illuminated and without any engineering/dispatch input is simply certifiably insane. It certainly blows your ASDA requirements out of the water!! Then, assuming that the defect is real, you'll have to land somewhere. In the event of any incident you'll buy a lot of lawyers new BMWs!!

Dispatch relief may be available but you'd need to analyse the planned operation very carefully, not just assume "she'll be right" during taxi.

23rd Mar 2010, 01:46
That's the way i would work being out of base (without tech assistance) with an antiskid failure during taxi or during startup:

1) NNC
2) take the MEL and DDG as references
3) update and modify takeoff performances accordingly (landing performances are already included in the NNC that refers to the advisory non normal landing distances)
4) continue the flight to destination (if the previous steps lead to safe operations)

At home base, during a flight to a non-base airport or an airport where no technical assistance is expected, i would come back to the stand and dispatch the aircraft with the antiskid INOP.

Gin Jockey
23rd Mar 2010, 04:21
You are kidding aren't you? Saying you would take the DDG as a "reference" is a bit light on. You either fully comply with the conditions is the DDG or you don't go, which is only possible if there is an (O) or an (M) or (O). If there is an (M) only (e.g. CB to be pulled and collared), then you must return to the gate.

It's not grey, it's very black and white.

Capt Chambo
23rd Mar 2010, 06:26
Different strokes for different folks.

On the ground our MEL prevails until we advance the thrust levers for T/O. In this case, it would be back to the gate for us, the engineers would do there bit and we would do ours, which include using full thrust, dry runway only, correcting the the T/O and landing gross weights, manual speedbrakes, and easy on the brakes initially in the event of an RTO.

Best thing to do is follow your company procedures.

23rd Mar 2010, 09:44
Regardless of your decision (or MEL applicability), once you have landed with the a/s u/s you then have significant performance penalties which could preclude departure from some airfields or the carriage of your payload. .It is always best to pullover and check the MEL and make a sensible decision as to go or taxi back. Having read the MEL for a/s u/s you will probably taxi back:eek:. It happened to me in BA once and they were totally unprepared for the performance implications which I think required use of a flap setting for take-off that was not in the books we carried. I made the point to them (like JmQ, I suspect) that I considered the NNC inadequate.

23rd Mar 2010, 10:36
The legal aspect will depend on the wording of your MEL and when it applies and also if you are useing a Boeing QRH as they do clearly state that you are expected to consult the Dispatch Deviations Guide prior to take off and apply any restrictions. This is why the NNC makes no mention of the take off case.

It would also be a good idea to check your landing perf at destination and alternate and to consider the implications to your company and to consult them and when you've done all that better make sure you still have enough fuel.

Regardless of legalities commonsense, self preservation and a duty of care towards your passengers and crew should make you stop and consider the implications.

We all know (or ought to know) that there is a severe performance penalty for an inop anti skid so to launch on your interpretation of a legal technicality without due consideration to the performance considerations would demonstate a stunning ignorance at best.

23rd Mar 2010, 11:31
Command decision then. If the wheels are still on the ground, and you are yet to commit the passengers and aircraft to the air, what is reasonable?

If you have a failure, and conduct the QRH NNC, this places the aircraft configuration into a "safe for the immediate future" position (and is primarily designed for flight). If you are still sitting on the ground, is it reasonable to spend two minutes looking up the MEL to see what the authorities have determined would be safe to allow an aircraft to depart with the same problem? Of course it is! :hmm:

If the MEL contains provisions for performance adjustments, would it be reasonable (on the ground you always have the time) to ignore those adjustments, and commit the passengers to the take-off without covering them? Of course NOT! :ugh:

If the MEL requires maintenance action to place the aircraft into a safer mode, is it reasonable to ignore that safety action, and still taxi out? Of course NOT! :ouch:

If you CAN meet all of the MEL provisions, and adjust the performance figures without returning to stand, is it then legal to depart without completing the paperwork (writing it up in the Tech Log, and having it signed off by an engineer - which starts the maintenance process of scheduling the repair, and leaves a record of the status of the aircraft should anything go wrong)? I would say YES. That is the reason for the rule stating that the aircraft has dispatched at push back.

Note: That doesn't mean that it is the best idea to depart. Part of being a professional pilot is not only to be safe, but to be efficient. An action can be safe, but terribly uneconomic.

Capt Pit Bull
23rd Mar 2010, 13:31
You need to watch your backside on things like this.

Its important to differentiate between cause and effect. The fact that a particular caution is lit is a symptom, its not a cause. Without engineering input its pretty difficult to ascertain if the problem is limited to to the system in question or whether you are looking at the tip of an iceberg.

The way I look at it any time a system flls over, there is an implied question mark over the power and data supplies to that system. 737 is kind of fading into the mists of time for me now, but off the top of my head:

1.) Maybe there is a faulty squad switch. If so, who knows what other systems could fail to transition to flight mode on take off, or vice versa on landing? Transponder, Pressurisation, idle floor, gear selection / warnings etc. You could find yourself with a christmas tree on lift off.

2.) Skid control valves work by releasing brake pressure. Do you really want a question mark over the condition of those valves?

Its one thing to take of with a system that has failed, where the cause has been identified and the system secured safe. Its another thing altogether to blast off with the aircraft in an indetermiante condition.

Whether the MEL applies legally or not is really a bit of a red herring imho, either way it doesn't absolve you from your general responsibility to ensure the aircraft is airworthy.


Max Angle
23rd Mar 2010, 15:57
either way it doesn't absolve you from your general responsibility to ensure the aircraft is airworthy.

Absolutely right, well put.

23rd Mar 2010, 16:15
I totally agree with Capt Pit Bull.

Our MEL says something like "The provisions of the MEL are applicable until the aircraft commences the flight, i.e. the point when an aeroplane begins to move under its own power for the purpose of preparing for takeoff.

Any decision to continue a flight following a failure or unserviceability which becomes apparent after the commencement of a flight must be the subject of pilot judgement and good airmanship. The Commander may continue to make reference to and use of the MEL as appropriate."

Just because you've commenced the flight (i.e. taxi) then you just can't ignore a failure like anti skid, or engine failure and press on regardless!

The "commences flight" bit is to cope with a failure which can sensibly be carried - something like a pack failure say, which may be required to be wire locked closed under the MEL and placarded "INOP", but you may dispatch with just the QRH procedure (i.e. selected off) completed for your sector.