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Questions about V1

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Questions about V1

Old 23rd May 2020, 12:37
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Originally Posted by safetypee
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,
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.
SafetyPee, read the conversation again. More flap BEFORE the take off roll commences great. Changing it in the middle of the roll is not something the FAA or Boeing would ever endorse..
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Old 23rd May 2020, 16:08
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Originally Posted by 8che
SafetyPee, read the conversation again. More flap BEFORE the take off roll commences great. Changing it in the middle of the roll is not something the FAA or Boeing would ever endorse..
Lets be clear what we are talking about here; you are barrelling down the RW with, for example, a V1 of 130 kts (I'm in an A320). Shortly after the "100 kts" call - say for arguments sake 110kts - the speed trend arrow goes from the top of the speed scale to zero and the CAS stagnates. The wind arrow on the PFD shows a significant and unforecast tailwind.The end of the RW approaches - whats to do? Clearly, your calculated performance is now out of the window and you are in survival mode - the FCTM/FCOM no longer helps.
TOGA - sure.
Rotate at 110kts - maybe.
Sit and wait for Vr - could be noisy and expensive - GS is by now way higher than the CAS
If an increased flap setting is available to aid the ac to fly - maybe.
Stop - no way.

Other positive contributions are of course welcome.
Cheers
mcdhu
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Old 23rd May 2020, 17:15
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The modelling representation of windshears in simulators has the same basis as that of the aircraft - measured data. But while the aircraft model is derived from aircraft data, the windshears (and indeed other things) are dervived from more general data. There are in fact a range of "canned" wind profiles derived from a number of real life events, and those can be used (they are also used in windshear warning/guidance certification tests).

I would be very cautious in assuming that the assumptions on which the aircraft performance calculations are based are themselves regulatory, especially in the operational world - just because Part 25 says to assume something doesn't mean part 121 (say) enforces it. I would also be very cautious about extrapolating those same performance assumptions outside their intended scope; there's nothing in part 25 about assuming any kind of windshear for the purpose of performance calculations - the closest there is would be the 0.5x/1.5x factor on STEADY wind, but that's hardly applicable to the shear case.
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Old 24th May 2020, 02:09
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It might be appropriate to keep in mind that the design and operational rules, inter alia, are based on rational statistical history relating to accidents and incidents

The rules (and, by inference, the SOPs which, largely, are based on the rules) do not provide anything like an every day guarantee that an aircraft heading off to the holding point will, in fact, successfully find its way to the other end of the flight planned for the day. History certainly indicates that the rules get it right a very high proportion of the time so they should be viewed as being not too bad overall - but not infallibly correct and appropriate.

Even with the bit of padding and fudge factoring which is embodied in the rules, if circumstances on the day get a little too far away from the presumed story, then one has to accept that, on such days, one really ought not to have got out of bed. On flights for which such applies, the rules don't really give us much comfort and the captain, yet again, finds that when he (she) looks to the left to seek guidance, there is only the well-known face reflected in the side window - once again, the captain realises that he (she) can be in a very lonely place. Sometimes, the captain is called on to take decisions for which some of the rationale can only be guesswork - that's the nature of command, unfortunately.

Windshear is one of those considerations for which the rules can be found wanting. If a pilot cannot accept the reality that flying is not a perfect activity and that risk cannot be regulated totally out of the equation then, perhaps, that pilot ought to seek alternative employment.

As a side comment, knowing who folks such as safetypee and mad (flt) scientist are, might I suggest that their (very experienced and competent) technical/operational expertise warrants that their counsel be considered ...

I think safetypee summed it up, if I might be permitted to quote - "The critical decision in potential wind-shear conditions is in the choice to takeoff, opposed to delay."
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Old 24th May 2020, 03:15
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Originally Posted by 8che
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.
To supplement the above. Windshear scenarios are typically based upon the FAA Windshear Training Aids (WTA) developed at the end of the last century and Microbursts are typically based upon either the NASA TM 85969 or the Royal Aircraft Establishment (RAE) models again from the last century. These are very much training tools/aids and generic in nature.
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Old 24th May 2020, 04:38
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I agree with John Tullamarine.It is impossible for SOPs to cover every eventuality. There are times when they are not appropriate to the situation and the captain must decide to deviate from them. This is an extreme measure and should only be done when there is no other option and when the pilot has sufficient knowledge to understand fully the implications of what he/she is doing. This is what command means. I can think of several examples.

Suppose on take-off at maximum weight in a four engine aircraft (a 747 with multiple landing gears) at a hot and high airfield, birds are ingested into both engines on the same side. Then, when airborne only a few feet above the ground, and barely able to climb, the co-pilot calls positive rate of climb, but the captain elects to leave the gear down until more speed and altitude has been gained. Non-standard, but his reasoning is that the extra drag of the open doors and wheel wells may well cause the aircraft to sink back towards the ground.

Suppose on final approach all engines suddenly stop. The captain elects to retract the flaps one notch. Non-standard, but the drag reduction is just sufficient to stretch the glide and make the airfield.

Suppose in mid-Atlantic, the underfloor cargo fire warning lights illuminate, the crew have reason to believe the warning is genuine and divert to the Azores. When they arrive the weather has deteriorated, the cross-wind has risen above limits and the cloud base has descended to below decision altitude. There is nowhere else to go and it is imperative to land. They do so successfully. All three examples were genuine events. It is not difficult to dream up other scenarios where such actions may be necessary.

And one more to ponder: the Qantas Airbus A380 at Singapore when the turbine disc exploded causing extensive damage and multiple unrelated warnings. In what order should the crew action the various procedures, which should be ignored and which have to be actioned?

Any serious captain should study his/her profession sufficiently so that he/she is prepared for such extreme eventualities.
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Old 24th May 2020, 09:16
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Check your documents for some wording. My company (and every one I have worked for) has something in the company documentation that roughly says:

“There cannot be a procedure for every scenario and nothing in these documents prevents the PIC from taking whatever action is necessary for the safe outcome of the flight”.
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Old 24th May 2020, 09:27
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Slight thread drift - into the air; re ZFT's comments on simulated wind shear models.
The serious incident (accident) reported and discussed in the link below shows the correlation of a real-world wind shear with a simulator training model. As I recall the origin of the FAA model 4 was the Dallas accident.
The report also enhances JT's and Bergerie's points about 'captaincy', 'Captains In Command'.

https://www.dropbox.com/s/51zkz0lznd...unter.pdf?dl=0

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Old 24th May 2020, 10:53
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As highlighted above, you need to exercise your airmanship.

I use to operate a Global from a 15000ft runway. You could take-off at maum (100,000lbs), positive rate, gear up, climb to 100ft, change your mind, gear down, Flap 30, land ahead stopping before the end. Yet, on the initial take-off run at V1 and above you are mandated to go - and would probably be criticised for aborting above it. You have to know your perf and understand exactly what and why it is telling you!
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Old 27th May 2020, 19:14
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Memory Items

At Takeoff:
If before V1: If there are significant variations in airspeed, and in airspeed trend below the indicated V1, reject the takeoff.
If windshear occurs during the takeoff roll, the aircraft may reach V1 later (or sooner) than expected.
The flight crew should ensure that there is sufficient runway remaining to stop the aircraft, if necessary.
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Old 28th May 2020, 03:31
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At V1 energy is your friend. Add engine thrust if able.

Your concerns are rough ground if overrun or inability to clear a high obstruction ahead.
I believe from the incident data that the former is a much higher probability of a bad day then the inability to clear a treeline etc. If you continue you will typically have more time to add energy and recover flying speed to clear obstacles. If you try stopping you have a much higher probability of serious aircraft damage.

I presume that you do think about this before you get into such a bind of decision
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Old 28th May 2020, 17:58
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S7pilot, "The flight crew should ensure that there is sufficient runway remaining to stop the aircraft,."
The crew can only know with certainty that there is sufficient runway for the situation as planned. In any other situations, e.g. stop after V1, then the statement (as a procedure) is meaningless because the crew cannot be sure.
In wind-shear / turbulent conditions the crew do not know how much distance has already been used ~ how much runway remains. The GS may not relate to IAS, thus the pre-takeoff performance calculations cannot be assured..

Re H Peacock's scenario; few pilots would know the actual takeoff ground roll given the range of possible scenarios - WAT, and additionally the effect of wind-shear.
Even fewer pilots know the landing distance required at max takeoff wt (and variability in wind-shear); thus there is no easy way to determine the distances required.
'You have to know your perf and understand exactly what and why it is telling you!'
Yes, but if the understanding is based on false assumptions then the performance is meaningless, and also the belief that you have a choice of options, or that the aircraft will stop on the runway.

Whilst lomapaseo's points are valid, the scenario should be considered (reframed) as independent situations.
The GO option in wind-shear, an extremely rare event, even more so with failure, it is a procedurally trained-for situation - with or without wind-shear.
An RTO before V1 is also a trained-for event which should result in a 'reasonably safe' outcome (very little margin).
However, a stop decision after V1 is not the same as a 'trained for' RTO. It may use similar procedures, but involves high risks, where procedures may not give a safe outcome. Actions must be considered as mitigations to reduce the magnitude of the accident. This is a significantly different viewpoint (frame of reference) which crews may overlook.

chx230, ask your management to explain this difficult situation.
A gentle reminder for them, that V1 is the speed at which the first stop action is taken - the decision has already been made.
QARs, (automatic analysis, etc) are based on recorded speeds and the outcome of action, e.g. brakes applied, but neither the recorders or analysis cannot know when you made the decision to stop (or go).
In any scenario, achieving V1 is a GO situation, there are no further decisions or alternative procedures for takeoff.
I sense that your management might not be ready for this type of discussion.

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Old 29th May 2020, 10:31
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If I might make a follow on comment in respect of PEI's post (and I do so cautiously, having a high regard for his background and experience), "normal" certification stuff is based on presumptions incorporated into the Design Standards (with a bit of fat here and there for mum and the kids and which serve us very well most of the time). However, if the conditions on the day vary significantly (and adversely) from those embodied in the presumptions, then things rapidly can get to the "all bets are off" stage.

Examples which come to mind include windshear and strong crosswind from the wrong side/OEI case on a min speed Vmcg-limited departure, and so forth. Either the Commander sticks with the trained protocol (windshear is a good case in question) or he/she may have to do something innovative eg with the strong crosswind/OEI situation. In the former, severely degraded performance capability may rapidly result in loss of control while, in the latter, there is high probability that control will be lost concurrent with the engine failure, albeit that the aircraft may well be somewhat above min V1.

Ergo, some days it just doesn't pay to get out of bed albeit folk such as Haynes, Sullenberger et al occasionally manage to pull it all together on the day. On other occasions, eg AF 4590, even though Marty (from what I could discern from available reading material) did everything he needed to do near perfectly, the aircraft just refused to sit up and perform the required tricks in its dreadfully degraded performance state.

As I am fond of observing, there are no guarantees, only probabilities and presumptions.
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Old 29th May 2020, 18:14
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A guess with no proof (assumption) or a guess with reasonable evidence (presumption).

John, thanks for your comments and thoughtful observation, which stirred more thoughts. 'Did my post represent what I intended', I think so.

However, as much as I detest trivial debate about words and meanings, in this context, what is the difference between 'presumptions' - your choice, and my use of 'assumptions'. *

Considering a scenario from an earlier post; - always use a wet V1, which might to some minds infer that there will be an 'additional' safety margin, but probably not as much as envisaged by the differences in speeds (call for perf engineer).

Thence 'presumption' represents an engineering, regulatory, management, view. A technical judgement before the event, credited with greater certainty in specific - as designed /calculated, operations.

Conversely crews relate to assumptions. Some held before an event - bias, erroneous knowledge - belief that requirements are understood; others from a real time evaluation of the situation as presented to them.
The latter may not have the same certainty as prior presumption, more often much less certainty. A wet V1 on a dry runway, or a wet V1 on a wet runway, but how wet; what is presumed vs what is assumed.

The gap between the two is a view of airmanship. **

Yet from OP#1, the difference could be that management's (we know best) after-the-event judgement, with FDR analysis, is biased by the presumption that crews will behave as in the calculated performance, rules, regulations, and trained for situations.
Whereas the crew have to assume that their assessment of the situation at the time is appropriate, and act accordingly - airmanship; there is no right or wrong, no guarantees, only probabilities and historical interpretation; either to learn from (assumptions) or chastise crews (presumptions).

I prefer to start with the crew making a reasonable judgement because they were there, at the time; so learn from them.

* The words assume and presume both mean that you take something for granted as being true, but the difference is based on how certain you are.
Assume is typically used in situations where someone takes something as the truth with a very low level of certainty or with no proof at all.
Presume usually involves a higher level of certainty and is used in situations where someone makes an educated guess based on reasonable proof or evidence.

Assumption is a noun related to the verb assume, and refers to the act of taking for granted or supposing something. Likewise, presumption is a noun related to the verb presume, and refers to a belief on reasonable grounds or probable evidence.


Presume and assume are often used interchangeably and have similar meanings. When you’re trying to decide which word to use, think about the level of certainty involved and whether it’s a guess with no proof (an assumption) or a guess with reasonable evidence (a presumption). Assume vs Presume

** My view of Airmanship in this post.

Do we presume or assume that the glass is half full, or half empty.
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