vmca/vmcg
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A similar question is very typical in EZY interviews, too.
I think they get those questions from a book: "The ACE pilot interview", I think it is titled. They use it in Cathay pacific interviews as well as in EZY and apparently, in RYR.
By the way, there are quite a few mistakes in that book, in my opinion. I had it for a while and I didn't like it very much.
If the initial question of this thread is looking for the answer to such an interview question, I don't recommend the answer in that book, unless the interviewers believe it, because it was wrong, if I recall correctly.
I think they get those questions from a book: "The ACE pilot interview", I think it is titled. They use it in Cathay pacific interviews as well as in EZY and apparently, in RYR.
By the way, there are quite a few mistakes in that book, in my opinion. I had it for a while and I didn't like it very much.
If the initial question of this thread is looking for the answer to such an interview question, I don't recommend the answer in that book, unless the interviewers believe it, because it was wrong, if I recall correctly.
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May I ask you the connection between both segments of your post in bold?
moderate V1-Vr split
consideration is the time taken to accelerate OEI from V1 to Vr which might be quite some knots difference.
but likely to depart the side of the runway with an out of control aircraft
... and all the while you are veering off the runway if you do not have adequate control over the deviation.
In some cases the problem can be addressed by having a high V1/Vr ratio so that the aircraft is off the ground by the time it gets to the Vmcg deviation limit. Some of the older UK certifications were approached in this manner.
Am I correct understanding such statement as
you are probably trying to simplify and generalise too much in your statement. Keep in mind that usually there is some extra control margin due to CG and runway surface providing a lower real world Vmcg than that specified under the certification conditions. The real point in question is that, with a strong crosswind, you MIGHT be in the situation of being below the real world Vmcg on the day. One needs to consider a range of factors to make an assessment. The consequent consideration is to look at how the pilot intends to manage the potential problem (if he chooses not just to ignore it).
moderate V1-Vr split
consideration is the time taken to accelerate OEI from V1 to Vr which might be quite some knots difference.
but likely to depart the side of the runway with an out of control aircraft
... and all the while you are veering off the runway if you do not have adequate control over the deviation.
In some cases the problem can be addressed by having a high V1/Vr ratio so that the aircraft is off the ground by the time it gets to the Vmcg deviation limit. Some of the older UK certifications were approached in this manner.
Am I correct understanding such statement as
you are probably trying to simplify and generalise too much in your statement. Keep in mind that usually there is some extra control margin due to CG and runway surface providing a lower real world Vmcg than that specified under the certification conditions. The real point in question is that, with a strong crosswind, you MIGHT be in the situation of being below the real world Vmcg on the day. One needs to consider a range of factors to make an assessment. The consequent consideration is to look at how the pilot intends to manage the potential problem (if he chooses not just to ignore it).
Just to add to J_T's comment on split V1/Vr:
On my previous plane, yes, the C-5, we had a chart showing the crosswind limits when "RCR" (AF milspeak for runway friction) was less than "wet". At lower RCRs, when V1 = Vr, there was little loss of crosswind capability. But, when V1<Vr, the crosswind limits got smaller quite quickly. From around 23 knots on "wet" to about 5 knots on low RCRs on contaminated runways. Control between V1 and Vr, while using aerodynamic controls to counter the OEI, ultimately control still depends on tire patch maintain adhesion with the pavement.
A maximum gross weight take-off from a wintry strong crosswind at RAF Mildenhall, with a large (say 12-15 knots) split between the two, was very enlightening of the problem. On a dry runway, OEI would be exciting!
GF
PS, Due Lockheed's intention and AF direction, performance was done in conformance with FAR 25, as of 1970. But some calculations were horrendously detailed, we even computed 4-engine take-off run. Which was surprisingly close to OEI critical field length.
On my previous plane, yes, the C-5, we had a chart showing the crosswind limits when "RCR" (AF milspeak for runway friction) was less than "wet". At lower RCRs, when V1 = Vr, there was little loss of crosswind capability. But, when V1<Vr, the crosswind limits got smaller quite quickly. From around 23 knots on "wet" to about 5 knots on low RCRs on contaminated runways. Control between V1 and Vr, while using aerodynamic controls to counter the OEI, ultimately control still depends on tire patch maintain adhesion with the pavement.
A maximum gross weight take-off from a wintry strong crosswind at RAF Mildenhall, with a large (say 12-15 knots) split between the two, was very enlightening of the problem. On a dry runway, OEI would be exciting!
GF
PS, Due Lockheed's intention and AF direction, performance was done in conformance with FAR 25, as of 1970. But some calculations were horrendously detailed, we even computed 4-engine take-off run. Which was surprisingly close to OEI critical field length.
still learning....
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Prior to retiring, I ran the three-engine ferry operation for my company. Many times we waited for a different runway with more favorable winds.
It's easy, "Good engine, good wind. Bad engine, bad wind."
It's easy, "Good engine, good wind. Bad engine, bad wind."
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Different appraoch to the old problem
The B787 has a system called TAP or Thrust Asymmetry Protection that recognizes large thrust to weight ratios during takoff and go around scenarios. It will reduce the power on the good engine up to 10% when below normal operating speeds to assist in maintaing control. In addition another system knoiwn as TAMS, Thrust Asymmetry Minimum Speed will give the pilot a visual cue regarding his airspeed vs. min control speed.
The B787 does not use the TAC as does the B777 for assisting in rudder control, but rather uses inherent FBW logic to assist in overcoming large rudder forces during engine out flight conditions.
The B787 does not use the TAC as does the B777 for assisting in rudder control, but rather uses inherent FBW logic to assist in overcoming large rudder forces during engine out flight conditions.
Last edited by Spooky 2; 30th Oct 2009 at 19:35.
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If you are operating a light twin and have an engine failure while airbourne it obviously makes no difference from which side the wind is coming from until of course you have to land. There are a few ways to tackle this, if the winds are light the easiest thing to do is glide in with no assymetric power, easy with plenty of runway. I say plenty of runway because you would want to aim deep as probably most pilots who fly only twins have probably lapsed in their ability to judge a glide. However if you are using power on the approach then you most definately want the wind from the same side as the live engine. Just try flying a twin in a crosswind and using assymetric power to assist the rudder. A fun skill to have in the bag, having done a lot of this it becomes natural but is a strange idea to get used to.
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Having read "Ace the Technical Pilot Interview" I'm unsure if what I wrote in my previous post in this thread is correct. Now I know this book is full of errors but I hope someone can clear this up for me. The book mentions the following:
Basically this says the opposite to what I thought, in the way that you'd prefer the crosswind to be from the dead engine.
...a failed critical number 1 engine will cause a yaw to the left. A crosswind component from the left will apply a restoring force to the aircraft's fuselage, whereas a crosswind from the right will aggravate the yawing moment further to the left due to the sideways force experienced on the right side of the aircraft's fuselage (which is from the right to the left).
Moderator
As general observations -
(a) engine numbering often starts from the left as viewed by the crew so one might expect a No 1 failure to be the left hand (outboard) engine giving a nose left yawing moment
(b) a left crosswind generally results in a nose left yawing moment, aggravating the effect of the failure.
(c) once the dynamics have settled down, you find yourself with a bootful of right rudder to control the yaw.
(d) the rudder input results in a lateral force to the left which results in a sideslip (equals drag and a small performance penalty) so it is desirable to add a little bank into the operating engine(s) to balance the sideslip. One notes that, for simplicity, this may be omitted on the basis that a small performance penalty may be preferable to a moderate increase in manipulative workload other than in critical circumstances.
(e) I don't think I incline to the book's story ...
(a) engine numbering often starts from the left as viewed by the crew so one might expect a No 1 failure to be the left hand (outboard) engine giving a nose left yawing moment
(b) a left crosswind generally results in a nose left yawing moment, aggravating the effect of the failure.
(c) once the dynamics have settled down, you find yourself with a bootful of right rudder to control the yaw.
(d) the rudder input results in a lateral force to the left which results in a sideslip (equals drag and a small performance penalty) so it is desirable to add a little bank into the operating engine(s) to balance the sideslip. One notes that, for simplicity, this may be omitted on the basis that a small performance penalty may be preferable to a moderate increase in manipulative workload other than in critical circumstances.
(e) I don't think I incline to the book's story ...
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Two tips.
Two tips which may help some or all of you.
Tip 1. Refers more to a twin than a quad. If you have an engine failure on the runway, on recognition, apply full rudder smoothly. Time is of the essence, you have probably displaced youself from the runway centre line and you are probably not pointing directly down the runway either. Application of full rudder, initially, is your best bet. If in the following seconds it is too much, just back it off and continue.
Tip 2. I don't ever remember being given a choice of runway in a heavy at an international airport, so cross wind is just a fact of life. New thinking is that if you have a gusty crappy crosswind, don't do a reduced thrust take off. Use you right as the signing captain to use all of the thrust and fuel you signed for. This also much reduces the chance of a tail strike when you are wallowing at 12 deg pitch up and the aircraft is still deciding whether it can be botherd to fly with an assumed temp of +63c.
Enjoy.
Tip 1. Refers more to a twin than a quad. If you have an engine failure on the runway, on recognition, apply full rudder smoothly. Time is of the essence, you have probably displaced youself from the runway centre line and you are probably not pointing directly down the runway either. Application of full rudder, initially, is your best bet. If in the following seconds it is too much, just back it off and continue.
Tip 2. I don't ever remember being given a choice of runway in a heavy at an international airport, so cross wind is just a fact of life. New thinking is that if you have a gusty crappy crosswind, don't do a reduced thrust take off. Use you right as the signing captain to use all of the thrust and fuel you signed for. This also much reduces the chance of a tail strike when you are wallowing at 12 deg pitch up and the aircraft is still deciding whether it can be botherd to fly with an assumed temp of +63c.
Enjoy.
