What is optimum v1 and improved v1
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engineering information and analysis to know how much of a range in excess of the published Vmcg that this would extend
Can only speak to those few test programs where I have had some involvement with Vmcg related exercises.
A principal measure, post failure, is the tracking deviation from centreline. As the speed reduces from the normal sort of routine speeds one uses, the deviation tends to be relatively stable until one gets near to Vmcg when it starts to increase. In the last few knots, and my observations put this in the 5 kt or so range, the deviation diverges quite rapidly to the point where it is outside the required measure.
Obviously, there may be variation with different Types but I imagine that my observations will not be too far away from the norm.
In the explanation below, no mention is made about an engine inoperative scenario.
Like a lot of certification stuff, one needs to read a bit between the lines for intent and, as you have done, refer to the ACs to find out what the FAA might have thought was relevant. One needs to keep in mind that the bulk of certification performance work relates to OEI rather than AEO.
Such items such as the following offer some insight -
(a) No takeoff made to determine the data required by this section may require exceptional piloting skill or alertness
(b) There may be no uncontrollable ground-looping tendency in 90-degree crosswinds, up to a wind velocity of 20 knots or 0.2 VSR0
(c) There must be a 90-degree crosswind component established that is shown to be safe for takeoff and landing on dry runways
(d) The airplane must exhibit satisfactory controllability and handling characteristics in 90-degree crosswinds at any ground speed at which the airplane is expected to operate.
(e) The applicant should demonstrate that exceptional skill is not required to maintain directional control on a wet runway with a ten-knot crosswind from the most adverse direction. For demonstration purposes, a wet runway may be simulated by using a nose wheel free to caster on a dry runway. Symmetric braking should be used during the demonstration, and both all-engines-operating and critical-engine-inoperative reverse thrust should be considered.
If your concern lies with a thought that the OEI case doesn't consider cross wind components, the above requirements would scarcely be satisfied ?
(I took the liberty of editing your post to replace the underlined text with italics .. I was getting a headache trying to read it)
Can only speak to those few test programs where I have had some involvement with Vmcg related exercises.
A principal measure, post failure, is the tracking deviation from centreline. As the speed reduces from the normal sort of routine speeds one uses, the deviation tends to be relatively stable until one gets near to Vmcg when it starts to increase. In the last few knots, and my observations put this in the 5 kt or so range, the deviation diverges quite rapidly to the point where it is outside the required measure.
Obviously, there may be variation with different Types but I imagine that my observations will not be too far away from the norm.
In the explanation below, no mention is made about an engine inoperative scenario.
Like a lot of certification stuff, one needs to read a bit between the lines for intent and, as you have done, refer to the ACs to find out what the FAA might have thought was relevant. One needs to keep in mind that the bulk of certification performance work relates to OEI rather than AEO.
Such items such as the following offer some insight -
(a) No takeoff made to determine the data required by this section may require exceptional piloting skill or alertness
(b) There may be no uncontrollable ground-looping tendency in 90-degree crosswinds, up to a wind velocity of 20 knots or 0.2 VSR0
(c) There must be a 90-degree crosswind component established that is shown to be safe for takeoff and landing on dry runways
(d) The airplane must exhibit satisfactory controllability and handling characteristics in 90-degree crosswinds at any ground speed at which the airplane is expected to operate.
(e) The applicant should demonstrate that exceptional skill is not required to maintain directional control on a wet runway with a ten-knot crosswind from the most adverse direction. For demonstration purposes, a wet runway may be simulated by using a nose wheel free to caster on a dry runway. Symmetric braking should be used during the demonstration, and both all-engines-operating and critical-engine-inoperative reverse thrust should be considered.
If your concern lies with a thought that the OEI case doesn't consider cross wind components, the above requirements would scarcely be satisfied ?
(I took the liberty of editing your post to replace the underlined text with italics .. I was getting a headache trying to read it)
Joined: Apr 2008
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John and Air Rabbit are spot on and correct; like in all segments of life there is some educated people; who learned the ins and outs of all the problematics; well outside the box of REQUIRED knowledge.
STICK TO THE MANUAL, and FLY the NUMBERS!! This is what you are paid for...( Hopefully)
STICK TO THE MANUAL, and FLY the NUMBERS!! This is what you are paid for...( Hopefully)
I have provided a link to a British Airtours crash many years back where this issue was discussed by the AAIB. On a 707 training flight during takeoff in a crosswind, the instructor closed the thrust lever of an engine at a critical moment. While there were other issues that led to the crash, the company policy of Engine out training in crosswinds was discussed.
http://www.aaib.gov.uk/cms_resources...8%20G-APFK.pdf
I have deleted some text from the quote to save typing as I could not copy and paste. Therefore this is not a completely direct quote below but I did put it in italics.
It states that For UK certification, Vmcg is established with a 7 knot crosswind component from the adverse side, the 'trade' for higher value varies considerably between types. A good conservative rule of thumb is to add 1.3 knots to Vmcg for every one knot of crosswind above 7 knots up to a maximum component of 15 knots around maximum landing weight. Further extrapolation is not advised because the greatly increased V1 will then be incompatible with the VR and V2 speeds. The 15 knot limit would 'lift'(increase) Vmcg by 11 knots for a Boeing 707.
Think about what they are saying. For every 1 knot of crosswind above the certified certified amount of crosswind that the aircraft had its Vmcg established(which is zero for most aircraft we fly), add 1.3 knots to Vmcg(each aircraft is different and aircraft weight is a factor as well) This value of 1.3 knots is what the CAA calls conservative but it makes the point. And even if for your own aircraft it is 30% less, this is still a 1 knot increase in VMCG for every knot of crosswind.
For the 707 under the conditions calculated by the CAA(near max landing weight), the Vmcg increased by 11 knots for what would be the equivalent of a 15 knot crosswind(23 knots in this case) for most certified airliners because Vmcg was determined with no crosswind for most airliners.
The CAA also does not go beyond, in this case 23 knots of crosswind(7 knot for certification in the UK plus 15 knots crosswind in addition), because as they state, Vmcg will be above Vr. Something to think about in your next strong crosswind takeoff. At Vr, you may be below your VMCG even if Vr is quite a bit above V1. And there is no real way of figuring out the particular details for your aircraft.
Last edited by JammedStab; 12th June 2014 at 05:46.
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This is a pet concern of most of us who are both pilots and ops engineers. I refer those interested to a search on the Vmcg topic across PPRuNe .. plenty of discussions.
However, one ought not to be unduly pessimistic about life, death and the universe in respect of Vmcg - for most considerations it is a boundary condition for other performance items.
As to Rules of Thumb -
(a) for twins (based on such formal OEM data as I have obtained) Vmcg should increase with crosswind at around 0.5kt/kt (specifically for rear fuse mounted engines but, probably, not too far off the mark for twins in general - alternatively pad towards the quad figure)
(b) for quads probably in the order of 1kt/kt or slightly more.
Main point is that book Vmcg is at the extreme low end of the routine operating scale so the small region where one might be exposed due to an increased crosswind is not visited much in routine operations. Add to this the observation that the situation and aircraft configuration probably will be less critical than for the book figure and one can be a little more comfortable.
Certainly one could take the view that the combination of a Vmcg limiting takeoff with a failure and in strong crosswinds is a rare event. In any case, it can be mitigated simply by the commander's saying "no way, Jose, we'll have a cup of coffee and wait for better conditions".
Vmcg and crosswind is a problem for very light takeoffs from very short runways without any clearway to play with. Most of the time this doesn't apply.
Where you have a bit more runway to play with, the easiest way to mitigate the risk is to schedule the speeds for a higher weight within the range permissible for the runway.
At Vr, you may be below your VMCG even if Vr is quite a bit above V1.
But only for a restricted region of the envelope as mentioned above in reasonably strong crosswinds with the "wrong side" failing. In general, this isn't a problem at all.
And there is no real way of figuring out the particular details for your aircraft.
The rules of thumb above are useful in the real world.
However, one ought not to be unduly pessimistic about life, death and the universe in respect of Vmcg - for most considerations it is a boundary condition for other performance items.
As to Rules of Thumb -
(a) for twins (based on such formal OEM data as I have obtained) Vmcg should increase with crosswind at around 0.5kt/kt (specifically for rear fuse mounted engines but, probably, not too far off the mark for twins in general - alternatively pad towards the quad figure)
(b) for quads probably in the order of 1kt/kt or slightly more.
Main point is that book Vmcg is at the extreme low end of the routine operating scale so the small region where one might be exposed due to an increased crosswind is not visited much in routine operations. Add to this the observation that the situation and aircraft configuration probably will be less critical than for the book figure and one can be a little more comfortable.
Certainly one could take the view that the combination of a Vmcg limiting takeoff with a failure and in strong crosswinds is a rare event. In any case, it can be mitigated simply by the commander's saying "no way, Jose, we'll have a cup of coffee and wait for better conditions".
Vmcg and crosswind is a problem for very light takeoffs from very short runways without any clearway to play with. Most of the time this doesn't apply.
Where you have a bit more runway to play with, the easiest way to mitigate the risk is to schedule the speeds for a higher weight within the range permissible for the runway.
At Vr, you may be below your VMCG even if Vr is quite a bit above V1.
But only for a restricted region of the envelope as mentioned above in reasonably strong crosswinds with the "wrong side" failing. In general, this isn't a problem at all.
And there is no real way of figuring out the particular details for your aircraft.
The rules of thumb above are useful in the real world.
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JammedStab
Sorry to be pedantic but it was being operated by British Airtours, an off-shoot of BEA. It was not BOAC!
Rather like the subjects being discussed on the thread on simulator training in cross-winds, it is essential for instructors to understand their machine's limitations. On that thread it is the limitations of the simulator as well as those of the aircraft. In this accident at Prestwick the instructor did not understand the certification standard for VCMG in a crosswind.
Sorry to be pedantic but it was being operated by British Airtours, an off-shoot of BEA. It was not BOAC!
Rather like the subjects being discussed on the thread on simulator training in cross-winds, it is essential for instructors to understand their machine's limitations. On that thread it is the limitations of the simulator as well as those of the aircraft. In this accident at Prestwick the instructor did not understand the certification standard for VCMG in a crosswind.
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Another European CAA has recognized the danger of assuming that V1 in a crosswind guarantees a safe outcome if a properly flown continuation of flight is performed with an engine failure at V1.
While air carrier commercial operations may have a small likelihood of this being an issue due to the good fortune of engine reliability, it appears to be a higher risk in the training environment.
http://www.transport.gov.mt/admin/up...no%2002_02.pdf
4. Performance Considerations
4.1 Training Captains must only simulate engine failure on take-off in crosswind conditions when they are certain that the speed at which the simulated failure is initiated will, in the prevailing conditions, allow an adequate margin of control.
4.1.1 Certifications under JAR-25 make no allowance for crosswind components in the calculation of VMCG. As general guidance, therefore, Training Captains in aeroplanes so certificated should not simulate engine failure below thegreater of:
(a) VI
and
(b) VMCG incremented by 1 kt per kt of crosswind component (to a maximum of 10 kt).
If (b) is the greater value, VI should not be increased but the engine failure
initiated at the appropriate speed above VI.
4.1.2 The advice of manufacturers’ training departments should be sought before engine failures are simulated in crosswind components greater than 10 kt, and in any case engine failures should never be simulated in crosswind components exceeding 15 kt, or on slippery or contaminated runways. Crosswind conditions make it difficult to monitor the trainee’s rudder input and to correct any degree of wrong or inadequate movement.
While air carrier commercial operations may have a small likelihood of this being an issue due to the good fortune of engine reliability, it appears to be a higher risk in the training environment.
http://www.transport.gov.mt/admin/up...no%2002_02.pdf
4. Performance Considerations
4.1 Training Captains must only simulate engine failure on take-off in crosswind conditions when they are certain that the speed at which the simulated failure is initiated will, in the prevailing conditions, allow an adequate margin of control.
4.1.1 Certifications under JAR-25 make no allowance for crosswind components in the calculation of VMCG. As general guidance, therefore, Training Captains in aeroplanes so certificated should not simulate engine failure below thegreater of:
(a) VI
and
(b) VMCG incremented by 1 kt per kt of crosswind component (to a maximum of 10 kt).
If (b) is the greater value, VI should not be increased but the engine failure
initiated at the appropriate speed above VI.
4.1.2 The advice of manufacturers’ training departments should be sought before engine failures are simulated in crosswind components greater than 10 kt, and in any case engine failures should never be simulated in crosswind components exceeding 15 kt, or on slippery or contaminated runways. Crosswind conditions make it difficult to monitor the trainee’s rudder input and to correct any degree of wrong or inadequate movement.
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ie one prefers to play with min speed failures in a simulator and keep a comfortable margin for the aeroplane.
Then there is the problem of simulator fidelity .. however, unless it's poor, most of those boxes with which I've played have been good enough for generic training .. which is the principal endorsement training aim for this region.
Generally, it is sufficient to give the student a long lasting wariness about needlessly exposing him/herself to Vmcg limiting takeoffs.
Then there is the problem of simulator fidelity .. however, unless it's poor, most of those boxes with which I've played have been good enough for generic training .. which is the principal endorsement training aim for this region.
Generally, it is sufficient to give the student a long lasting wariness about needlessly exposing him/herself to Vmcg limiting takeoffs.
