Obstacle Clearance comes last?
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Obstacle Clearance comes last?
Scenario: Runway analysis shows that the aircraft is obstacle limited and the specific flap retract altitude (third segment) reflects this limitation. Crew do not know the position of the controlling obstacle - just that the weights displayed are obstacle limited. Notwithstanding that this is a regulatory limiting weight, an operator directs that in event of failure/problem/fire etc after V1, all Phase One actions (Recall in some types) must be completed before the third acceleration segment is started even though this may mean that the third segment is commenced at a greater altitude than called for in the runway anaylsis.
The rationale for this policy is that the crew should direct their priorities toward securing the problem because it may overload them to commence level acceleration (obstacle clearance requirement) while at same time carrying out Phase One actions to secure the failed engine.
Surely it should not be beyond the capabilities of a trained crew to meet the obstacle clearance criteria while simultaneously carrying out the appropriate engine shut down drills?
Is the company directed policy flawed in this regard? Either the aircraft is obstacle limited or not. You can't have it both ways - or can you?
The rationale for this policy is that the crew should direct their priorities toward securing the problem because it may overload them to commence level acceleration (obstacle clearance requirement) while at same time carrying out Phase One actions to secure the failed engine.
Surely it should not be beyond the capabilities of a trained crew to meet the obstacle clearance criteria while simultaneously carrying out the appropriate engine shut down drills?
Is the company directed policy flawed in this regard? Either the aircraft is obstacle limited or not. You can't have it both ways - or can you?
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BizJetJock ...
Not necessarily ..
(a) consider a fourth segment limiting obstacle .. you drive the second segment higher and the fourth segment will be pushed out .. perhaps enough to compromise the sums. Now, the gross to net margin gives you considerable fat in the fourth segment .. but you will be eating into the margin in this case.
(b) if there are turns involved further out, you may be compromising the plan
(c) it is likely that the third segment may be engine limited.
.. just some thoughts ...
Not necessarily ..
(a) consider a fourth segment limiting obstacle .. you drive the second segment higher and the fourth segment will be pushed out .. perhaps enough to compromise the sums. Now, the gross to net margin gives you considerable fat in the fourth segment .. but you will be eating into the margin in this case.
(b) if there are turns involved further out, you may be compromising the plan
(c) it is likely that the third segment may be engine limited.
.. just some thoughts ...
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Turns
john_tullamarine, isn't this why operators will (and have to)promulgate Emergency Turn Procedures away from limiting obstacles?
Also consider that the acceleration phase if commenced at a higher altitude than normal will still intercept the final segment on the same gradient - just at a higher point.
Draw a diagram and extend the second segment up a bit - draw a line across to meet the final segment. It will provide the same distance for acceleration without compromising any segments.
If clearance was compromised, no operator would consider accomplishing drills in the second segment!
Also consider that the acceleration phase if commenced at a higher altitude than normal will still intercept the final segment on the same gradient - just at a higher point.
Draw a diagram and extend the second segment up a bit - draw a line across to meet the final segment. It will provide the same distance for acceleration without compromising any segments.
If clearance was compromised, no operator would consider accomplishing drills in the second segment!
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Minuteman,
(a) Turning away from an obstacle is an option .. but not a requirement. Consider that the radius of turn complicates the analysis and there is a climb gradient decrement (usually somewhere in the vicinity of 0.6 percent for a 15 degree bank turn). In many cases there is just not enough room to lay out the turn prior to an obstacle and the only way out is to constrain weight enough to clear it vertically. I can remember one difficult runway where I spent some considerable time trying umpteen different (and variously interesting) escape tracks before it became apparent that the various penalties ended up predicating a straight ahead climb over the obstacle as being the best payload option ....
(b) if the aircraft is anywhere near WAT limits, you will see a measurable distance penalty if you drive the second segment higher .. no hard and fast rule as to where it becomes worse off for the fourth segment .. just a matter of doing the sums until one gets a good enough feel for the particular AFM to be able to foretell the story in advance. As the second segment gradient is not constant .. as the aircraft goes up .. the gradient capability goes down ... with the very shallow gradients we are looking at .. a small gradient penalty for a given third segment height can result in loads more distance run.
(c) If clearance was compromised, no operator would consider accomplishing drills in the second segment! ... you exhibit a refreshing degree of idealism, good sir ......
(a) Turning away from an obstacle is an option .. but not a requirement. Consider that the radius of turn complicates the analysis and there is a climb gradient decrement (usually somewhere in the vicinity of 0.6 percent for a 15 degree bank turn). In many cases there is just not enough room to lay out the turn prior to an obstacle and the only way out is to constrain weight enough to clear it vertically. I can remember one difficult runway where I spent some considerable time trying umpteen different (and variously interesting) escape tracks before it became apparent that the various penalties ended up predicating a straight ahead climb over the obstacle as being the best payload option ....
(b) if the aircraft is anywhere near WAT limits, you will see a measurable distance penalty if you drive the second segment higher .. no hard and fast rule as to where it becomes worse off for the fourth segment .. just a matter of doing the sums until one gets a good enough feel for the particular AFM to be able to foretell the story in advance. As the second segment gradient is not constant .. as the aircraft goes up .. the gradient capability goes down ... with the very shallow gradients we are looking at .. a small gradient penalty for a given third segment height can result in loads more distance run.
(c) If clearance was compromised, no operator would consider accomplishing drills in the second segment! ... you exhibit a refreshing degree of idealism, good sir ......
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There seems little point in performance engineers going to all the technical and regulatory trouble to ensure the runway analysis is valid in terms of obstacle clearance when the company policy is dictated by ops management that the pilot must disregard obstacle clearance requirements in favour of checklist reading priorities. Because that is exactly what happens when the obstacle directed third segment is thrown out of the window simply to satisfy checklist actioning.
Have pilots lost basic flying ability skills so much in todays automation environment that policy makers feel that the pilots cannot be trusted to do two things at once ie fly the aeroplane in level flight as well as actioning checklists?
Have pilots lost basic flying ability skills so much in todays automation environment that policy makers feel that the pilots cannot be trusted to do two things at once ie fly the aeroplane in level flight as well as actioning checklists?
Menen, I agree with the doing TWO things at once.
The problem gets bigger as at some stage you will have to reconfigure flap and then climb. So do you interrupt a Phase One Checklist and call for a flap selection or compromise your performance by holding the flap and either climbing or accell past optimum climb speed?
The guidance I have been given is you MAY compromise your 3rd segment by raising the second segment alt esp if you have a max engine time limitation.
My thoughts are if you are performing poorly after a post V1/ Pre Accell segment it will take some time to get to that alt...hopefully enough to complete the Phase one. Then proceed as normal
If you are light/cold/etc and performing well then you will reach your accell alt before Phase Ones are complete BUT you will have a healthly margin above any limitations.
My personal thoughts ...if its still turning leave it alone, Ifs its not then what ever you do isn't going to get it back. if it's turning and BURNING then have a quick think and make a DECISION based on as many variables as your brain can accept in that split second and then stick to it
The problem gets bigger as at some stage you will have to reconfigure flap and then climb. So do you interrupt a Phase One Checklist and call for a flap selection or compromise your performance by holding the flap and either climbing or accell past optimum climb speed?
The guidance I have been given is you MAY compromise your 3rd segment by raising the second segment alt esp if you have a max engine time limitation.
My thoughts are if you are performing poorly after a post V1/ Pre Accell segment it will take some time to get to that alt...hopefully enough to complete the Phase one. Then proceed as normal
If you are light/cold/etc and performing well then you will reach your accell alt before Phase Ones are complete BUT you will have a healthly margin above any limitations.
My personal thoughts ...if its still turning leave it alone, Ifs its not then what ever you do isn't going to get it back. if it's turning and BURNING then have a quick think and make a DECISION based on as many variables as your brain can accept in that split second and then stick to it
