Delayed rotation compromise
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Delayed rotation compromise
Hello all!
So the other day, we were taking off from a very long 4000m runway. Just before commencing the roll, we noticed many birds flying just at some height above the center of the runway. A lot of them.
And just after V1, as Rotate was called out, it became clear that if a normal rotation was done then, at the 3°/sec rate, it was certain that we would right fly through a dense bird concentration.
We decided of rotating very slowly, just to pass them still on the runway, and after that, very slowly rotating, we lifted off and were clear of them. Takeoff and climb progressed normally.
Now a question arised. Was this delayed rotation, lifting off much later than the performance calculation, outside of the minimum gradient limits?
We still had a lot of runway ahead, more than a 1/3rd when we lifted off.
My comprehension is, since we're not field limited, with our take off weight, our V1 and Vr were at those speeds just because it was more than enough. But since we were still with a long runway ahead, I cannot think why we can't delay the rotation, even if obstacles and a 2nd segment obstacle clearance limit were of concern.
As I see, as long as we lift off passing at 50ft above the clearway or the other end threshould, our second segment gradient will be obstacle free.
Am I right or missing something?
In other words, taking off from the middle of the runway or very near the end, doesn't affect obstacle clearance and 2nd segment requirements, since we are still taking off from the runway and complying with the requirements.
I would like to see your thoughts in this... In that situation it was the best decision since, better take off with all engines even delaying lift off, than to rotate precisely at the calculated speed, and face the real threat of one or even 2 engines failing.
So the other day, we were taking off from a very long 4000m runway. Just before commencing the roll, we noticed many birds flying just at some height above the center of the runway. A lot of them.
And just after V1, as Rotate was called out, it became clear that if a normal rotation was done then, at the 3°/sec rate, it was certain that we would right fly through a dense bird concentration.
We decided of rotating very slowly, just to pass them still on the runway, and after that, very slowly rotating, we lifted off and were clear of them. Takeoff and climb progressed normally.
Now a question arised. Was this delayed rotation, lifting off much later than the performance calculation, outside of the minimum gradient limits?
We still had a lot of runway ahead, more than a 1/3rd when we lifted off.
My comprehension is, since we're not field limited, with our take off weight, our V1 and Vr were at those speeds just because it was more than enough. But since we were still with a long runway ahead, I cannot think why we can't delay the rotation, even if obstacles and a 2nd segment obstacle clearance limit were of concern.
As I see, as long as we lift off passing at 50ft above the clearway or the other end threshould, our second segment gradient will be obstacle free.
Am I right or missing something?
In other words, taking off from the middle of the runway or very near the end, doesn't affect obstacle clearance and 2nd segment requirements, since we are still taking off from the runway and complying with the requirements.
I would like to see your thoughts in this... In that situation it was the best decision since, better take off with all engines even delaying lift off, than to rotate precisely at the calculated speed, and face the real threat of one or even 2 engines failing.
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Essentially, in either of the cases, you would be perfectly safe to do what you did - considering obstacles.
Here is the TC CARs reference: Part V - Airworthiness Manual Chapter 525 - Transport Category Aeroplanes - Transport Canada
Keep reading to about 525.121 if you want to know about climb gradient requirements after takeoff.
If you want the FAA FARs reference, take off the first 5 and that's what it is. Ie: FAR 25.107 - Electronic Code of Federal Regulations:
You'll find the CARs is essentially a carbon-copy of the FARs.
Here is the TC CARs reference: Part V - Airworthiness Manual Chapter 525 - Transport Category Aeroplanes - Transport Canada
Keep reading to about 525.121 if you want to know about climb gradient requirements after takeoff.
If you want the FAA FARs reference, take off the first 5 and that's what it is. Ie: FAR 25.107 - Electronic Code of Federal Regulations:
You'll find the CARs is essentially a carbon-copy of the FARs.
You may have exceeded your tyre speed limit, or brake energy limit, however.
(Acceptable in this case, under the Captain's emergency authority.)
Your gradients would have been OK (two engines adding energy throughout the extended time to rotation.)
I would also have submitted an ASR (which would explain the event to the Flight Data Monitoring team) and helped the statistical "heads up" about the bird problem at that runway.
(Acceptable in this case, under the Captain's emergency authority.)
Your gradients would have been OK (two engines adding energy throughout the extended time to rotation.)
I would also have submitted an ASR (which would explain the event to the Flight Data Monitoring team) and helped the statistical "heads up" about the bird problem at that runway.
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First, great replies!
The climb gradient and performance was OK as your replies mention.
However when someone else cast a doubt and a worry was, in case of an engine failure and a single engine initial climb after lift off, would the aircraft still be able to comply with the minimum gradient requirement and obstacle clearance, in that case of delayed rotation, or even a "worst case", rotating near the end of the runway?
The climb gradient and performance was OK as your replies mention.
However when someone else cast a doubt and a worry was, in case of an engine failure and a single engine initial climb after lift off, would the aircraft still be able to comply with the minimum gradient requirement and obstacle clearance, in that case of delayed rotation, or even a "worst case", rotating near the end of the runway?
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However when someone else cast a doubt and a worry was, in case of an engine failure and a single engine initial climb after lift off, would the aircraft still be able to comply with the minimum gradient requirement and obstacle clearance, in that case of delayed rotation, or even a "worst case", rotating near the end of the runway?
Delayed rotation means that you will have a higher speed on the climb out which means you'll be able to have a higher climb rate/gradient meaning better obstacle clearance.
But FAR 25 and CAR 525 don't specifically deal with 'obstacle clearance'. They deal with aircraft performance. To ensure obstacle clearance, if you're IFR, you must follow the appropriate procedures. The standard departure is 1/2 statute mile visibility and has the following conditions: cross the departure end of the runway at 35', climb at 200'/NM until you reach your enroute altitude and maintain runway heading until 400' AAE. Those procedures are based on the obstacle clearance requirements that are part of the US TERPS, TC TP-308, and ICAO documents. The standard Obstacle Clearance Surface that applies to the standard 1/2 mile departure is a 40:1 slope. 40:1 = 152' of vertical climb for every 1 nautical mile. No obstacle are to penetrate that OCS for a standard departure, ie: a 200'/NM climb gradient. That provides at least 48'/NM of clearance from all obstacles. As long as you abide by the instrument departure procedure for the runway you're using, you will be guaranteed obstacle clearance.
Also, regarding OEI climb performance, the obstacle clearance requirements do not change. Depending on what part of FAR or CAR you're operating under, you may or may not need to ensure compliance with the instrument departure procedure assuming OEI. But either way, I can ensure you that just because the regulations say you don't need to ensure obstacle clearance with OEI, you NEED to ensure OEI obstacle clearance - the obstacles don't just disappear when you lose an engine, they will be waiting for you if you decide to go below the appropriate altitude!
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Every second you have two engines producing thrust after V1 you're generating a lot better performance vs. losing an engine at V1. Min climb gradient should not be an issue.
Last edited by misd-agin; 6th May 2012 at 20:55. Reason: added second sentence
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Be careful - as the old sci fi show put it "danger, Will Robinson".
it was certain that we would right fly through a dense bird concentration.
not good
We decided of rotating very slowly
probably a smart move in the circumstances - PROVIDED you don't lose one and there are no nasty close in obstacles. Very much a case of horses for courses.
However, the reject might also be a good option in some situations and potentially better than keeping on with the takeoff - the SYD 727 mishap provides some useful thoughts on the relative go/stop considerations (I don't know if TAA had the nosewheel brakes mod but, with that, stopping on the 727 was awesome).
Seeing you had such a runway pad, had you given any thought to abandoning the takeoff instead of delaying the rotation ? .. noting that this presumes that you have some knowledge of your stopping performance above the particular V1.
Was this delayed rotation, lifting off much later than the performance calculation, outside of the minimum gradient limits?
almost certainly yes. Whether that is dangerous or not on the day depends on the runway environment and the takeoff calculations.
I cannot think why we can't delay the rotation, even if obstacles and a 2nd segment obstacle clearance limit were of concern.
depends entirely on the specifics of the runway. Almost certainly you will be below the calculated NFP for a period. The potential consequences will depend on the specific circumstances and whether you lose an engine .. and where
as long as we lift off passing at 50ft above the clearway or the other end threshould, our second segment gradient will be obstacle free.
in general, absolutely NOT so. End of strip obstacle clear gradients can be quite significant and well outside the typical heavy aircraft's OEI capability. While you may well have a benign runway with negligible EOS profile problems, generally that is not the case.
What you appear to be doing is confusing obstacle clear gradients with both WAT and on the day OEI/AEO gradients.
In that situation it was the best decision since
very likely the case, being mindful of Chesley Sullenberger's mishap.
it was certain that we would right fly through a dense bird concentration.
not good
We decided of rotating very slowly
probably a smart move in the circumstances - PROVIDED you don't lose one and there are no nasty close in obstacles. Very much a case of horses for courses.
However, the reject might also be a good option in some situations and potentially better than keeping on with the takeoff - the SYD 727 mishap provides some useful thoughts on the relative go/stop considerations (I don't know if TAA had the nosewheel brakes mod but, with that, stopping on the 727 was awesome).
Seeing you had such a runway pad, had you given any thought to abandoning the takeoff instead of delaying the rotation ? .. noting that this presumes that you have some knowledge of your stopping performance above the particular V1.
Was this delayed rotation, lifting off much later than the performance calculation, outside of the minimum gradient limits?
almost certainly yes. Whether that is dangerous or not on the day depends on the runway environment and the takeoff calculations.
I cannot think why we can't delay the rotation, even if obstacles and a 2nd segment obstacle clearance limit were of concern.
depends entirely on the specifics of the runway. Almost certainly you will be below the calculated NFP for a period. The potential consequences will depend on the specific circumstances and whether you lose an engine .. and where
as long as we lift off passing at 50ft above the clearway or the other end threshould, our second segment gradient will be obstacle free.
in general, absolutely NOT so. End of strip obstacle clear gradients can be quite significant and well outside the typical heavy aircraft's OEI capability. While you may well have a benign runway with negligible EOS profile problems, generally that is not the case.
What you appear to be doing is confusing obstacle clear gradients with both WAT and on the day OEI/AEO gradients.
In that situation it was the best decision since
very likely the case, being mindful of Chesley Sullenberger's mishap.
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If you rotated at a VR higher than the one of your obstacle level off weight limit,then yes,you were outside your perf.
Increased V2 as someone mentionnecd only increases the initial climb if V2is less than max V2(around 1.35VS).
Increased V2 as someone mentionnecd only increases the initial climb if V2is less than max V2(around 1.35VS).
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only increases the initial climb if V2is less than max V2(around 1.35VS).
You will get a better gradient for quite an increase in V2 at the expense of field distance.
However, that is not the point in question.
The main problems with an ad hoc overspeed takeoff is that
(a) the flight path will be under that calculated from lift off until the improved higher gradient intersects the calculated gradient. It could be a case of there be dragons in that region.
(b) the higher speed results in larger turn radius if the departure involves turns to manage obstacles. This also tends to result in the subsequent flight path being sufficiently displaced laterally from that calculated to put the aircraft out of the calculated obstacle splay region. Again, it could be a case of there be dragons
You will get a better gradient for quite an increase in V2 at the expense of field distance.
However, that is not the point in question.
The main problems with an ad hoc overspeed takeoff is that
(a) the flight path will be under that calculated from lift off until the improved higher gradient intersects the calculated gradient. It could be a case of there be dragons in that region.
(b) the higher speed results in larger turn radius if the departure involves turns to manage obstacles. This also tends to result in the subsequent flight path being sufficiently displaced laterally from that calculated to put the aircraft out of the calculated obstacle splay region. Again, it could be a case of there be dragons
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Why would you start the take-off at all?
"Just before commencing the roll, we noticed many birds flying just at some height above the center of the runway."
warning: slf-generated content here:
Why would you start your take-off at all in that case?
Wouldn't calling the bird-control team be a better option?
Sorry, as a SLF, I would prefer NOT being launched into a potential disaster - you were stationary and should have stayed that way until the birds were scared off.
warning: slf-generated content here:
Why would you start your take-off at all in that case?
Wouldn't calling the bird-control team be a better option?
Sorry, as a SLF, I would prefer NOT being launched into a potential disaster - you were stationary and should have stayed that way until the birds were scared off.
Last edited by freqslf; 7th May 2012 at 06:52. Reason: grammar
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Just before commencing the roll, we noticed many birds flying just at some height above the center of the runway.
I agree with freqslf, you should not have started the takeoff roll if you knew that there was wildlife in the runway environment or if you knew you couldn't follow your normal takeoff procedures.
I recommend reading this publication: TP 13549 - Sharing the Skies - Transport Canada
Specifically in this chapter (Chapter 10 ? Solutions ? Pilots - Transport Canada) they discuss that you would be in violation of CAR 602.01 "Reckless or negligent operation of aircraft".
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Some (many in fact) years ago I lined up for take off in a Viscount on a long runway. We were light weight due it being a positioning flight. We spotted large flocks of birds several hundred yards ahead on the runway. We delayed take off and requested the fire engine crew to scare them off using the water cannon. This was successful and ten minutes we began the take off roll.
Just before VR we ran head on into a whole bunch of birds initially unseen that had been feeding on the grass flight strip on each side of the runway and which got airborne as we neared them. There were several impacts but no indications of power loss from the four engines.
We rejected the take off at above VR while still on the ground of course and without using brakes deliberately used the full remaining length of 6000 ft to pull up using the propeller ground-fine position which was very effective at high speed. We initially thought prop ground fine had failed to operate as there was a noticeable absence of the ground fine engine noise normally heard in a landing roll. Deceleration was excellent however and the prop ground fine noise came in within a few seconds. We later realised the reason for the perceived delay in hearing ground fine come in was that at that relatively high speed, it takes a finite time for the propellers to turn in their hubs from the take off angle through into the ground fine angle.
Runway inspection revealed 24 dead birds - while the aircraft inspection revealed a few blood smears but no damage. We departed after the inspection and there were no problems on the flight.
The reason we aborted was that everything happened in a flash and with a mile of runway ahead and hearing the multiple strikes it seemed a good idea to stop. Staying off the brakes was the option we took in view of excess stopping distance available. In fact the brakes were quite cold after we returned to the tarmac.
The Viscount incident happened some time after the fatal Lockheed Electra accident in USA where the aircraft hit a large flock of birds during initial climb after take off and lost nearly all power - subsequently crashing into Chesapeake Bay (I think that was the name). The instant decision to abort the Viscount take off roll may have been a subconscious recollection of the Electra accident - but who knows!
Just before VR we ran head on into a whole bunch of birds initially unseen that had been feeding on the grass flight strip on each side of the runway and which got airborne as we neared them. There were several impacts but no indications of power loss from the four engines.
We rejected the take off at above VR while still on the ground of course and without using brakes deliberately used the full remaining length of 6000 ft to pull up using the propeller ground-fine position which was very effective at high speed. We initially thought prop ground fine had failed to operate as there was a noticeable absence of the ground fine engine noise normally heard in a landing roll. Deceleration was excellent however and the prop ground fine noise came in within a few seconds. We later realised the reason for the perceived delay in hearing ground fine come in was that at that relatively high speed, it takes a finite time for the propellers to turn in their hubs from the take off angle through into the ground fine angle.
Runway inspection revealed 24 dead birds - while the aircraft inspection revealed a few blood smears but no damage. We departed after the inspection and there were no problems on the flight.
The reason we aborted was that everything happened in a flash and with a mile of runway ahead and hearing the multiple strikes it seemed a good idea to stop. Staying off the brakes was the option we took in view of excess stopping distance available. In fact the brakes were quite cold after we returned to the tarmac.
The Viscount incident happened some time after the fatal Lockheed Electra accident in USA where the aircraft hit a large flock of birds during initial climb after take off and lost nearly all power - subsequently crashing into Chesapeake Bay (I think that was the name). The instant decision to abort the Viscount take off roll may have been a subconscious recollection of the Electra accident - but who knows!
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There were several impacts but no indications of power loss from the four engines.
We rejected the take off at above VR while still on the ground of course and without using brakes
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sometimes overthinking in flying is dangerous.
don't hit things, keep a safe flying speed, everything is replaceable except people.
so much stuff about gradient, tyre speed etc.
sheesh....after 37 years in flying I've watched genius engineers flying planes and become fascinated with aileron displacement while they were flying into the side of a mountain.
I am glad however to see one reference to the idea of using a higher Vrotate in order to better protect yourself in a potential wind shear situation. Thats only been published since the middle 1970's.
ACT...think later...you might be flying too fast to take time to think...if you act wrong...well, maybe you wonj't have to worry next time
don't hit things, keep a safe flying speed, everything is replaceable except people.
so much stuff about gradient, tyre speed etc.
sheesh....after 37 years in flying I've watched genius engineers flying planes and become fascinated with aileron displacement while they were flying into the side of a mountain.
I am glad however to see one reference to the idea of using a higher Vrotate in order to better protect yourself in a potential wind shear situation. Thats only been published since the middle 1970's.
ACT...think later...you might be flying too fast to take time to think...if you act wrong...well, maybe you wonj't have to worry next time
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Jesus Christ, and you think I'm dangerous!
This is commercial aviation not Top Gun, we aren't "turning and burning" at warp factor snot down in the weedysphere or avoiding SAMs over the jungle.
The first lesson I learnt in flying was if something goes wrong, sit on your hands for two seconds before you rush in to a mistake.
This has served me well. But then again I'm not American.