Decision point or speed?
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Decision point or speed?
G'day all,
The mob I work for fly out of very short strips. During the take off brief there are always different ideas on using a decision point or speed. The op's manual is a bit grey in this area.
Do you use a Decision point, speed or both ie.
We will continue the take off once passed the windsock and above red line. If we have a failure below one of those points we abort the take off.
Thanks for your help.
The mob I work for fly out of very short strips. During the take off brief there are always different ideas on using a decision point or speed. The op's manual is a bit grey in this area.
Do you use a Decision point, speed or both ie.
We will continue the take off once passed the windsock and above red line. If we have a failure below one of those points we abort the take off.
Thanks for your help.
Spit Murphy
It’s been a while since I flew a piston twin but I use to use a decision point on long strips and a decision speed from short strips. The logic in this was that if I had runway in front of me and I could safely land back down on it, it was safer to land the thing than take the problem into the air where it could possibly get ugly.
It’s been a while since I flew a piston twin but I use to use a decision point on long strips and a decision speed from short strips. The logic in this was that if I had runway in front of me and I could safely land back down on it, it was safer to land the thing than take the problem into the air where it could possibly get ugly.
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Speed and Distance for Me
I was given some very good and simple advice by an old pilot friend years ago for getting out of short, or performance degrading, strips, viz:
This advice was complementary to consulting the aicraft P-charts.
I have found this rule of thumb to be quite workable over the years, but have never really tested it's validity or integrity against the advice of others.
So, I'd also be interested in any comments on this method.
If you havn't achieved three-quarters of your calculated TOSS by the runway half-way point, then abort!
I have found this rule of thumb to be quite workable over the years, but have never really tested it's validity or integrity against the advice of others.
So, I'd also be interested in any comments on this method.
QSK?
Just curious to how you worked out that this advice was complementary to P-charts.
404 Titan
What kind of decision points/speeds did you use?
Curious as I haven't had to land bigger aircraft into smaller strip but I'm sure the day will come soon
Would also like to know what kind of decision points/speeds are used by pilots of singles too.
Cheers
Just curious to how you worked out that this advice was complementary to P-charts.
404 Titan
What kind of decision points/speeds did you use?
Curious as I haven't had to land bigger aircraft into smaller strip but I'm sure the day will come soon
Would also like to know what kind of decision points/speeds are used by pilots of singles too.
Cheers
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Very interesting topic this. As a freshly rated light twin driver I have thought about this quite a bit.
I was taught a decision speed. Where i'm based there is plenty of runway, so our decision speed is increased to Vyse (ie: after rotation) so if an engine quits before this speed but after rotation, procedure is to close the throttles and land on remaining runway available. Although a decision point would work just as well i reckon, and maybe even more appropriate for a longer strip.
Out of shorter strips you don't have that luxury, and i'd use a speed, the max decision speed being rotate speed. Although my multi-engine command column is in single figures so i'm no authority
Unless i'm missing something what decision?
I was taught a decision speed. Where i'm based there is plenty of runway, so our decision speed is increased to Vyse (ie: after rotation) so if an engine quits before this speed but after rotation, procedure is to close the throttles and land on remaining runway available. Although a decision point would work just as well i reckon, and maybe even more appropriate for a longer strip.
Out of shorter strips you don't have that luxury, and i'd use a speed, the max decision speed being rotate speed. Although my multi-engine command column is in single figures so i'm no authority
Would also like to know what kind of decision points/speeds are used by pilots of singles too.
One thing that just using a decision speed is that it does not take into account acceleration. If you're not accelerating normally (due to altitude, surface condition, winds or slope) waiting until you have a specific speed may see you off the end of the strip. Using both a decision speed (Go/No go) for an engine failure and a decision point (Go/No Go) for acceleration is the best option.
Now I was taught and have used the 3/4 Vtoss by the halfway point on the strip as a great guide to whether you are accelerating at a rate to achieve the required takeoff performance. This of course, is applicable to any aircraft, regardless of the number of engines.
If you want to know more about decision points etc, I recommend reading the F.E. Potts guide to Bush Flying. See this link
. This book covers a lot of issues about operating from small strips which I havent seen covered elsewhere.
Now I was taught and have used the 3/4 Vtoss by the halfway point on the strip as a great guide to whether you are accelerating at a rate to achieve the required takeoff performance. This of course, is applicable to any aircraft, regardless of the number of engines.
If you want to know more about decision points etc, I recommend reading the F.E. Potts guide to Bush Flying. See this link
. This book covers a lot of issues about operating from small strips which I havent seen covered elsewhere.
Ever thought of reading the Aircraft Flight/Operating Manual.
I know the C402 used to have in Emergency Procedures - Engine Failure on Take-off below 95 knots - ABORT, above 95 knots - CONTINUE.
So my opinion use a speed not a decision point.
Recently shown video where statistics indicate that pilots that try to re-land on remaining runway after engine failure above V1 are worse off than those that elect to continue and do a circuit and re-land.
I know the C402 used to have in Emergency Procedures - Engine Failure on Take-off below 95 knots - ABORT, above 95 knots - CONTINUE.
So my opinion use a speed not a decision point.
Recently shown video where statistics indicate that pilots that try to re-land on remaining runway after engine failure above V1 are worse off than those that elect to continue and do a circuit and re-land.
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Spit Murphy,
It may help a little if you provide some clarification on what your definition of a short strip is as most of the other posts have all mentioned long and shorts strips? Where you'retalking about might come in handy too.
Some short strips (550m and less), as in the Torres Straits, IMO deserve to have a decision point rather than a speed. This is based on being able to stop on the remaining rwy if a failure occurs prior to the chosen point, or having a failure past (but<Vdec/yse) that point then getting airborne, being able to lower the nose, and gain all valuable airspeed and hopefully keep control. This is in preference to aborting a take-off post rotation and conducting a ditching or forced landing.
Obviously there are locations where you do not have the luxury of being able to descend (or land) after the end of the rwy, in this instance I too would use Vr because I'd prefer to have a fighting go at saving the a/c than just chopping the power and putting it into the trees.
Hope this helps a little.
Blown.
It may help a little if you provide some clarification on what your definition of a short strip is as most of the other posts have all mentioned long and shorts strips? Where you'retalking about might come in handy too.
Some short strips (550m and less), as in the Torres Straits, IMO deserve to have a decision point rather than a speed. This is based on being able to stop on the remaining rwy if a failure occurs prior to the chosen point, or having a failure past (but<Vdec/yse) that point then getting airborne, being able to lower the nose, and gain all valuable airspeed and hopefully keep control. This is in preference to aborting a take-off post rotation and conducting a ditching or forced landing.
Obviously there are locations where you do not have the luxury of being able to descend (or land) after the end of the rwy, in this instance I too would use Vr because I'd prefer to have a fighting go at saving the a/c than just chopping the power and putting it into the trees.
Hope this helps a little.
Blown.
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Blown Seal
I would definitely agree with you there.
When taking off from Darnley Island (approx 400m), I used to choose a decision point, beyond which, I would commit to the take-off, even if the failure occured before Vr.
The reason for this was that there is a rather steep drop off at the end of the strip, so rather than aborting and not coming to a complete stop on the runway, I would prefer to use the 200 foot drop-off at the end of the strip to accelerate the aircraft, and then if not climbing, a controlled descent in a level attitude onto the beach or the water's edge.
Anyway, that's just what I used to do.
BW
I would definitely agree with you there.
When taking off from Darnley Island (approx 400m), I used to choose a decision point, beyond which, I would commit to the take-off, even if the failure occured before Vr.
The reason for this was that there is a rather steep drop off at the end of the strip, so rather than aborting and not coming to a complete stop on the runway, I would prefer to use the 200 foot drop-off at the end of the strip to accelerate the aircraft, and then if not climbing, a controlled descent in a level attitude onto the beach or the water's edge.
Anyway, that's just what I used to do.
BW
ROB-x38,
I realise that this thread is more in tune with twin ops but what I would like to know is whether the 3/4 TOSS by half strip etc would also work in a single.
There'd have to be a point where the A/C would just not reach desired performance for take-off and "the decision" would be to abort the take-off.
Have known of a couple of singles to go off the end while on a "comfortable" strip and would like to know of a proven method so I can save myself from being a stat one day
By "proven" I mean, who did and how were the numbers crunched from P-charts.....if at all.
I realise that this thread is more in tune with twin ops but what I would like to know is whether the 3/4 TOSS by half strip etc would also work in a single.
There'd have to be a point where the A/C would just not reach desired performance for take-off and "the decision" would be to abort the take-off.
Have known of a couple of singles to go off the end while on a "comfortable" strip and would like to know of a proven method so I can save myself from being a stat one day
By "proven" I mean, who did and how were the numbers crunched from P-charts.....if at all.
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To Bull and Blown Seal,
I might have read your post wrong but what happens if you take off from Darnley or Mabuiag and have an engine failure past your decision point but below Vmca. You can't stop before the end of the runway and if you decide to keep going you will not have any rudder control. That is why I tend to use a decision point with speed also. I might be missing something here and that is why I asked for advice.
After re-reading your post I think you guys sort of do the same as what I am doing. I think I would keep it straight as best I could and fly it of the strip in ground effect.
Thanks for the advice everyone.
I might have read your post wrong but what happens if you take off from Darnley or Mabuiag and have an engine failure past your decision point but below Vmca. You can't stop before the end of the runway and if you decide to keep going you will not have any rudder control. That is why I tend to use a decision point with speed also. I might be missing something here and that is why I asked for advice.
After re-reading your post I think you guys sort of do the same as what I am doing. I think I would keep it straight as best I could and fly it of the strip in ground effect.
Thanks for the advice everyone.
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It has been a while, but from memory, the VMCA for an Islander was only 39 knots, and this was generally achieved well before the decision point. (I also preferred to have full power before releasing the brakes in these situations)
I always felt that a rejected take-off which resulted in an over-run at low speed, would almost certainly be fatal at Darnley, whereas continuing would hopefully be more controllable and therefore survivable.
I am just glad that I never had to put this theory into practice!
BW
I always felt that a rejected take-off which resulted in an over-run at low speed, would almost certainly be fatal at Darnley, whereas continuing would hopefully be more controllable and therefore survivable.
I am just glad that I never had to put this theory into practice!
BW
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Turbantime:
I fly a single and I have found from my experience that the 3/4 Vtoss by the runway mid-point works very effectively; and Bevan 66's post would appear to confirm this. The 50% Vtoss at the 40% runway point as mentioned by Not_Another_Pot is a new one to me, and one that I haven't tried. Somewhere in my collection is a magazine article on the "science" behind the 75/50 rule. If I find it, I'll PM you.
Wrt to your query on my eariler post, probably bad wording on my part. All I was trying to say is that, firstly, the pilot must still consult the P-Charts on the day to determine TODR and the relevant Vtoss, then apply the 3/4 TOSS by 50% distance rule of thumb.
I realise that this thread is more in tune with twin ops but what I would like to know is whether the 3/4 TOSS by half strip etc would also work in a single.
Wrt to your query on my eariler post, probably bad wording on my part. All I was trying to say is that, firstly, the pilot must still consult the P-Charts on the day to determine TODR and the relevant Vtoss, then apply the 3/4 TOSS by 50% distance rule of thumb.
To prove the 75% Vtoss by 1/2 strip length requires a bit of mathematics.
Assuming constant acceeration, at the 1/2 way point in your takeoff roll;
V1 = SQRT(V2^2/ 2)
where V1 = 1/2 way speed and V2 is Vtoss.
(Using newtons second law of motion).
Putting in some numbers, with a Vtoss of 75 knots;
V1 = 53 knots.
Now this is awfully close to 3/4 of Vtoss which is 56 knots. Now most of us cannot do this sort of maths in our head, so this rule of thumb gives reasonably accurate answers. So if you pass mid way on a strip with less than 56 knots, abort or you'll leave the end. If you pass mid way with more than that figure, you have room to spare - go.
Being in a single or twin will not make any difference. If a donk lets go after the mid point, your acceleration will reduce (or stop completely if you are in a single) and depending on length you will end up off the end, or may have enough to climb away.
This rule of thumb is good enough for me.
Bevan..
Assuming constant acceeration, at the 1/2 way point in your takeoff roll;
V1 = SQRT(V2^2/ 2)
where V1 = 1/2 way speed and V2 is Vtoss.
(Using newtons second law of motion).
Putting in some numbers, with a Vtoss of 75 knots;
V1 = 53 knots.
Now this is awfully close to 3/4 of Vtoss which is 56 knots. Now most of us cannot do this sort of maths in our head, so this rule of thumb gives reasonably accurate answers. So if you pass mid way on a strip with less than 56 knots, abort or you'll leave the end. If you pass mid way with more than that figure, you have room to spare - go.
Being in a single or twin will not make any difference. If a donk lets go after the mid point, your acceleration will reduce (or stop completely if you are in a single) and depending on length you will end up off the end, or may have enough to climb away.
This rule of thumb is good enough for me.
Bevan..
Decision point or speed?
It's a good idea to use both.
Unless you are flying a Learjet, there is a couple of seconds between those speeds.
You check your (precalculated) 50% runway length speed prior to rolling, then if this is exceeded, continue to your V1 speed, etc.
It's not hard and gives a very good indication as to how your aircraft is performing reasonably early in the take-off run.
Rule of Thumb #12 in The Axioms of Flight states, "Abort the takeoff if 70% of takeoff velocity is not attained within 50% of available runway"
Personally, I think the figure of 75% is far easier to mentally calculate and will also put you on the safer side.
It's a good idea to use both.
Unless you are flying a Learjet, there is a couple of seconds between those speeds.
You check your (precalculated) 50% runway length speed prior to rolling, then if this is exceeded, continue to your V1 speed, etc.
It's not hard and gives a very good indication as to how your aircraft is performing reasonably early in the take-off run.
Rule of Thumb #12 in The Axioms of Flight states, "Abort the takeoff if 70% of takeoff velocity is not attained within 50% of available runway"
Personally, I think the figure of 75% is far easier to mentally calculate and will also put you on the safer side.
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Decision point - based on my assessment of speed, height and rate of climb will be where I decide that the land ahead option is no longer available.
Single engine speed is a factor - if everthing goes my way we may continue to fly or
controlled or uncontrolled flight into terrain
Marginal length strips are a serious compromise.
Single engine speed is a factor - if everthing goes my way we may continue to fly or
controlled or uncontrolled flight into terrain
Marginal length strips are a serious compromise.
turbantime
Not sure how those that fly out of short strips can use a decision point. In any piston twin on a short strip, your decision to go or not go is going to be made base on whether you have attained Vyse or not, i.e. will the aircraft perform? By the time you have attained Vyse at a place like Darnley or Mabuiag you will have insufficient runway to land on straight ahead. You are going to need more than 100 ft if you are going to trade height for speed if you elect to go before Vyse. Making a decision to go before you have reached Vyse is fraught with danger. In all piston engine twins there is a grey area between Vtoss and Vyse where if something goes wrong with an engine, the aircraft will not perform assuming ISA conditions and an aircraft at MTOW. Unfortunately all flight manuals that I have seen only give one figure for Vyse, so it makes it difficult to determine what the real Vyse is if you are lighter than MTOW or colder than ISA. Conditions much hotter than ISA in many piston twins have shown that the aircraft won’t perform on one engine, period. You are going to have to use the good engine to make a forced landing.
As for using a decision point. I only ever used it out of Cairns or Townsville, as the strips were very long. The decision point must always be the same point over the ground as Vyse or beyond it and there must be sufficient runway to land straight ahead. If you can’t meet these requirements then you are going to have to use Vyse, i.e. a decision speed and accept that if an engine fails before this speed you are going to have to make a forced landing with the good engine taking you there.
Not sure how those that fly out of short strips can use a decision point. In any piston twin on a short strip, your decision to go or not go is going to be made base on whether you have attained Vyse or not, i.e. will the aircraft perform? By the time you have attained Vyse at a place like Darnley or Mabuiag you will have insufficient runway to land on straight ahead. You are going to need more than 100 ft if you are going to trade height for speed if you elect to go before Vyse. Making a decision to go before you have reached Vyse is fraught with danger. In all piston engine twins there is a grey area between Vtoss and Vyse where if something goes wrong with an engine, the aircraft will not perform assuming ISA conditions and an aircraft at MTOW. Unfortunately all flight manuals that I have seen only give one figure for Vyse, so it makes it difficult to determine what the real Vyse is if you are lighter than MTOW or colder than ISA. Conditions much hotter than ISA in many piston twins have shown that the aircraft won’t perform on one engine, period. You are going to have to use the good engine to make a forced landing.
As for using a decision point. I only ever used it out of Cairns or Townsville, as the strips were very long. The decision point must always be the same point over the ground as Vyse or beyond it and there must be sufficient runway to land straight ahead. If you can’t meet these requirements then you are going to have to use Vyse, i.e. a decision speed and accept that if an engine fails before this speed you are going to have to make a forced landing with the good engine taking you there.
QSK?
Thanks for the clear up, should have understood that that's what you meant to say
Bevan666,
Those numbers work quite well, I'm the kind of person that likes proof before trying rules of thumbs out (it instills more confidence in me)
404 Titan,
After thinking about the topic, I am too in line with thinking that twin ops would need a decision speed and that speed would be Vyse......and the rest would be left to as "on the day decision" which'd be covered in the take-off brief...ie more than sufficient runway, so land back on it.....or the 200 ft drop off which would allow further acceleration etc
Cheers for taking the time guys
Thanks for the clear up, should have understood that that's what you meant to say
Bevan666,
Those numbers work quite well, I'm the kind of person that likes proof before trying rules of thumbs out (it instills more confidence in me)
404 Titan,
After thinking about the topic, I am too in line with thinking that twin ops would need a decision speed and that speed would be Vyse......and the rest would be left to as "on the day decision" which'd be covered in the take-off brief...ie more than sufficient runway, so land back on it.....or the 200 ft drop off which would allow further acceleration etc
Cheers for taking the time guys
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Very Relevant
Great Topic.
NAP has it right...
It really is a combination of both. In the operation of jet aircraft as in the piston twin it is a speed...BUT WHAT WE ARE LOOKING AT WHEN WE CONSULT THE GRAPHS IS A SPEED WHICH ALLOWS US SUFFICIENT DIRT/BITUMEN IN METRES TO STOP!!
If you think of it as having the brakes stuck on, you might get to the desired speed when well into the trees. So the best approach is to remember that the speed can be deceptive and use a combination of speed and a distance, be it 40% of the field length or such and if you havent achieved that speed or the acceleration required, jump on the brakes!!!
Be safe!
NAP has it right...
It really is a combination of both. In the operation of jet aircraft as in the piston twin it is a speed...BUT WHAT WE ARE LOOKING AT WHEN WE CONSULT THE GRAPHS IS A SPEED WHICH ALLOWS US SUFFICIENT DIRT/BITUMEN IN METRES TO STOP!!
If you think of it as having the brakes stuck on, you might get to the desired speed when well into the trees. So the best approach is to remember that the speed can be deceptive and use a combination of speed and a distance, be it 40% of the field length or such and if you havent achieved that speed or the acceleration required, jump on the brakes!!!
Be safe!