Questions about V1
 

Hi all. I have a question about v1. Assuming I am rolling for take off. At the moment I reach V1, I encounter a severe wind shear. The airspeed suddenly drop below V1. Is it right that I should continue take off once the airspeed reach V1, and no matter the current speed is?

That's why pilots get paid the big bucks (hah!).

The theory says if you don't continue after reaching V1, you'll run off the runway end. But in a lift-killing windshear (head to tail)? You might have trouble reaching VR/V2 and getting off the runway either.

See AeroMéxico Connect Flight 2431. They tried to continue, crashed back to earth, overran the runway end anyway - amazingly with no deaths.

Thank you for your reply! Except the hazard wind shear may cause. What does the regulation say? Can I continue take off though the current speed is below v1, but it once reached v1 moment ago.

The regulations say the captain is responsible for the safety of the flight.

It depends on how your type does performance calcs. The type I fly, for example, has a wet V1 that is always 10kts(ish) below Vr, regardless of runway length, because it is a Vgo not a Vstop. Your decision based on circumstances - As previous poster says, that’s what you get paid for!

I totally agree that pilot should take responsibility for safety. But the situation in our country is very different. I will loose my job if I violate the regulation, even though that may lead to a better result. You can’t image that they download the QAR for every flight, and evaluate all my movement and decision second by second. So I am so care about that whether I violate the regulation if continue take off when the current speed is below v1 but once reached v1 before. We usually use BFL v1, and we can choose v1 max and v1 min.

There is no right answer to your question. It's really that simple. Your calculated V1 is invalid because of an external factor. Boeing provide some advice in their FCTM but it all comes back to crew judgement. BTW, we all live with QAR. Just use care and sound judgement and you'll be fine.

As others have said, there's judgement involved. Consider that continuing the takeoff allows for EF recognised at V1 - so, in the highly likely event that you retain all engines, you do have some margin (even BFL) if you continue. Consider margin between your normal liftoff speed and Vmu, Vs and V2, availability of additional thrust if using flex/assumed temp, or even fixed derate in this case - i.e. windshear = firewall thrust. It's also true that in many situations, if you reject above V1 you will stop before the end of the runway (how often are you right up against your RTOW on a long runway?, consider factoring of wind and allowance for pilot technique). Judgement and SA.

The guidance that springs to mind in this instance is, delay rotation until no later than 2,000 ft from the runway end. Seems like in most situations continuing would be the most appropriate option.

Another example may be more proper for what I am concerning. When I take off in a bumpy day. The airspeed is kinda up and down during rolling. I get one engine inoperative at v1, I choose to continue. But I don’t notice that when I add power from flex to rated, the airspeed has come back below v1 already. They find this in QAR. Can I still keep my job? You know it is a bbbbbbig issue to make GO decision when the speed is below v1. So I really want to figure out if I am exempt or not for the airspeed once reached v1

FFS. End of.

What Boeing says...
 

From our -1
After Go Speed

– MAX thrust.

– If still on the runway consider delaying rotation, run-way permitting. In no case should rotation be delayed beyond the 1,000 feet remaining mark.

Best answer


V1 is not a decision speed, it’s a go speed, an airspeed fluctuation does not count

If using increased V2 performance, the V speeds will be artificially high so its a bonus if you have an idea of what speed the ac will actually fly at. On the 320, for the same weight, temp etc, it was possible (in my day) to have V speeds that differed by 30kts on different runways (120 - 150kts).

So:
Consider TOGA
More flap to reduce stall speed?
Rotate when above 'flying speed'

Its not your day, but you might just get away with it.
mcdhu

chx230, et al, consider the overall context, the larger picture.

The critical decision in potential wind-shear conditions is in the choice to takeoff, opposed to delay.
Having decided to takeoff, then the V1 question in part answered; normal procedures with wind-shear precautions - max power, expect delayed liftoff, unusual instrument indications, etc *.

Whilst a 'paper' what-if scenario is not impossible, in practice a pilot is unlikely to see or appreciated the indications in a real wind-shear encounter. These situations highjack the mind, thus greater need to revert to trained-for, pre-conscious procedures.
V1 is V1, having achieved it, GO. Training must be for a GO minded operation.
Don't let the paper / sim / training gurus hijack realism, common sense.

and: to muddy the water - speed checks at 80 kts, what if one system fails after that, how would you know, who calls speed / V speeds. Is P2 ASI high or P1 low, … GO.
If it doesn't feel right, check and fly pitch-power; that should be part of any pre takeoff wind-shear briefing *.

and: whatever fatalistic outcome is envisaged, you chose that outcome in deciding to takeoff.

* https://www.faa.gov/documentLibrary/...ar/AC00-54.pdf

More flap ?? on the take off roll in wind shear ? Are you sure about that ? More flap will have just killed your climb angle for the hard bits after the runway plus changing the shape of the wing in a dynamic wind shear condition not good.

The poster is showing classic “Eastern” fear culture symptoms. Fear cultures kill resilience. Just operate with your best common sense. Look at it this way, the company will fire you for not following the rules and they will fire you for following the rules if it ends badly. You therefore can never win so do what you feel is the best you can on the day and at least you will walk away with your conscience clear.

8che - I'm not in this to argue, but more to provide options for considerations. Tried this in the sim a few times with a variety of variables. As you say, you have to do something except to sit and wait for V1 to appear (which it might not).

Cheers
mcdhu

This is a company culture problem. You do the best you can with the information you have. If you are subsequently fired, so be it. Far better to be fired after you did the best you could, rather than being fired after you dithered and second guessed yourself.

More importantly: Far better to be fired having saved the passengers and aircraft than to end up making a smoking hole in the ground because you were concerned about what the company would do to you.

chx230
There is no specific regulation that tells you to do one way or the other. Airbus somewhere says in general about WS on takeoff if you feel you can stop within remaining RW then stop but not specifically for such a case. If runway length is not very critical you should stop because reaching Vr and V2 is not the only problem wind shear can create. It could be worse once airborne. If ASDA was critical hit TOGA and take your chances in the air. Regulation wise I don't think you can be faulted for either of them.

Fair enough but its not an option and a dangerous suggestion so I have to call it out. The number one rule of wind shear recoveries is don’t change the config. Please don’t believe everything you see in a simulator. While a level D sim will almost certainly contain the actual fight modelled data of an airframe that is or was in service, the modelling of external environmental conditions is a pure manufactured mathematical model and so can only ever be preprogrammed. It can never therefore accurately model real world environmental and aircraft response. In short it ain’t and never will be the real aircraft response, just the best simulation.

8che, et al, "More flap ?? on the take off roll in wind shear ?"
Precautions on take off are discussed on page 38-39 of the FAA reference #14.
Re flap, 'more flap provided greater performance for WS encounters on the runway, but lesser flap settings provided better performance for in-the-air WS encounters'.
An aircraft and situation dependent compromise - resolved by delaying departure.

Re "…so do what you feel is the best you can on the day", this is a judgement based on knowledge, experience, training, guidance, etc, which must be balanced with a healthy respect of 'fear'.
This can be described as airmanship or common sense, neither of which has universal meaning, interpretation, or application. The best on the day is safe, again delay departure.

AerocatS2A, :ok:
Culture, etc. A reoccurring issue; in a perfect world we would not be fired, or if imperfect, we continue working for the wrong company - needs must.
Thus in the real world, pilots' require the judgement of Solomon and the skills of a 'Nelsonian eye'.

With an intolerant operator, for wind-shear conditions, protracted start and taxi procedures, or if pressured at the runway - a 'fictitious', intermittent, cargo door warning (the sort that an officious P2 doesn't see.)
Return to stand, have the door checked - by P2, outside in the wind, rain, and thunder.

Then seek views on wether the runway might be flooded - s/he would have to go outside agin for a 'puddle stomp test', or place 2 cents on the ground to judge water depth.

Wind-shear conditions and a flooded, limited distance, runway; a most likely combination for cb activity.

Thats 2 cents of experience; two people making sense of the situation.