why not stabalise engines with brakes on?
Guest
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Several posts on this thread refer to "especially if the aircraft's light" and or/ "short runways".
For me the consideration is not clear. Are you considering that if light and performing a rolling takeoff that a greater percentage of the TODA will be used prior to setting takeoff power than if heavy?
------------------
Clarrie
For me the consideration is not clear. Are you considering that if light and performing a rolling takeoff that a greater percentage of the TODA will be used prior to setting takeoff power than if heavy?
------------------
Clarrie
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Tom775257,
The run-up you mentioned was probably for icing considerations. With our RR engines we must run-up the engines to 60% N1 for 10 seconds whenever an icing condition at 0C OAT and below. If they did run for 30 seconds I can only assume that they were receiving there take-off clearance at that moment and chose to leave the power up rather than pull it back and to idle and forward again seconds later. No it should not have anything to do with the engine failure as if they were concerned about an engine problem they would not have departed especially with a twin!
Clarrie, I don't totally understand your point but take-off's are designed to use as much of the runway as practical and therefore if light we would use a reduced thrust take-off.
The run-up you mentioned was probably for icing considerations. With our RR engines we must run-up the engines to 60% N1 for 10 seconds whenever an icing condition at 0C OAT and below. If they did run for 30 seconds I can only assume that they were receiving there take-off clearance at that moment and chose to leave the power up rather than pull it back and to idle and forward again seconds later. No it should not have anything to do with the engine failure as if they were concerned about an engine problem they would not have departed especially with a twin!
Clarrie, I don't totally understand your point but take-off's are designed to use as much of the runway as practical and therefore if light we would use a reduced thrust take-off.
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747FOCAL,
I would be extremely interested in Boeing documentation to back up your claim of 600-700 feet.
We are presently the only operator in the world who still operates ALL models of the B747, including the B747-SP. We presently proclaim that the difference between standing and rolling takeoffs, when expressed in distance is negligible. This data is directly from the manufacturer.
Now you tell us that we are wrong?????
Mutt
I would be extremely interested in Boeing documentation to back up your claim of 600-700 feet.
We are presently the only operator in the world who still operates ALL models of the B747, including the B747-SP. We presently proclaim that the difference between standing and rolling takeoffs, when expressed in distance is negligible. This data is directly from the manufacturer.
Now you tell us that we are wrong?????
Mutt
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It is, of course, very satisfying to ex-fighter pilots' souls to stand on the brakes and set max. thrust in a 4-jet with min. permitted fuel, rotate briskly at Vr and then climb at V2 giving the local area the 'sound of freedom'! We can do it with 80000 lb of thrust in an aircraft weighing about 200 000 lb - and boy, does it go!! But not something that the travelling public would like to experience, I imagine, nor something that the fun-detectors would condone either!
[This message has been edited by BEagle (edited 27 May 2001).]
[This message has been edited by BEagle (edited 27 May 2001).]
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In 737 simulator with crew from SE Asia. Their company procedure was the PNF called " Stabilized" after PF had set the throttles, then once the call was made the PF would shove open the power for take off. I suggested to them that a specific call was not needed - just use your eyes to see the N1 were stabilized. That did not work, and during the exercise the call was always made.
So I quietly instructed PNF to " forget" to call stabilized. The PF then opened up to "stabilized" power and motoring past the 1500 ft marker around 30 knots still at low powerlooked accusingly at the PNF and said " Hey! You have forgotten to call" Stabilized!"....
So much for commonsense.
So I quietly instructed PNF to " forget" to call stabilized. The PF then opened up to "stabilized" power and motoring past the 1500 ft marker around 30 knots still at low powerlooked accusingly at the PNF and said " Hey! You have forgotten to call" Stabilized!"....
So much for commonsense.
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Clarrie
You note that -
Several posts on this thread refer to "especially if the aircraft's light" and or/ "short runways" (and wonder at this ...)
The concern is one of the dynamics of the acceleration in a limiting case (ie minimum runway available compared to runway required) - clearly, if the situation is one with significant excess runway, then the worry is rather lessened.
If an aircraft is heavy then there is
(a) a relatively high breakaway thrust required to commence rolling
(b) a reduced acceleration with whatever the particular aircraft can put out at rated thrust.
In the event that the pilot spins up and advances the throttles (thrust levers if you must) without undue delay, iaw the AFM assumptions, then, by the time that the aircraft has moved any significant distance in a rolling start, rated thrust is set and the overall result is similar to what might be obtained with a standing start on the brakes.
If the aircraft is light, then the situation is quite different and a pilot must exercise great care in setting thrust. Centaurus' tale above presents a useful example of the problem, albeit in an endorsement setting.
Cpdude
I find your statement that takeoffs are designed to use the maximum extent of the runway rather innovative but, I suggest, a little wide of your operations engineers' intent.
You note that -
Several posts on this thread refer to "especially if the aircraft's light" and or/ "short runways" (and wonder at this ...)
The concern is one of the dynamics of the acceleration in a limiting case (ie minimum runway available compared to runway required) - clearly, if the situation is one with significant excess runway, then the worry is rather lessened.
If an aircraft is heavy then there is
(a) a relatively high breakaway thrust required to commence rolling
(b) a reduced acceleration with whatever the particular aircraft can put out at rated thrust.
In the event that the pilot spins up and advances the throttles (thrust levers if you must) without undue delay, iaw the AFM assumptions, then, by the time that the aircraft has moved any significant distance in a rolling start, rated thrust is set and the overall result is similar to what might be obtained with a standing start on the brakes.
If the aircraft is light, then the situation is quite different and a pilot must exercise great care in setting thrust. Centaurus' tale above presents a useful example of the problem, albeit in an endorsement setting.
Cpdude
I find your statement that takeoffs are designed to use the maximum extent of the runway rather innovative but, I suggest, a little wide of your operations engineers' intent.
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John_tullamarine,
I agree with CPDUDE, most of our takeoffs use fixed derates combined with assumed temperature thrust reductions. We are therefore planning to use up most of the runway. The B727 isnt as flexible as some newer aircraft, but with the B744 we can reduce the takeoff thrust by upto 45%. Therefore making a light aircraft field length limited on even the longest runways.
Mutt
I agree with CPDUDE, most of our takeoffs use fixed derates combined with assumed temperature thrust reductions. We are therefore planning to use up most of the runway. The B727 isnt as flexible as some newer aircraft, but with the B744 we can reduce the takeoff thrust by upto 45%. Therefore making a light aircraft field length limited on even the longest runways.
Mutt
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Mutt,
Of course you can convert a non-limiting takeoff into a limited example ... but who in his right mind would do so ? The majority of operators in my ken avoid going quite that far - and having been on the receiving end of the inquisitorial system, I suggest that that would be a difficult situation to argue convincingly at the coronial inquest with a couple of QCs breathing down your neck.
Operational scheduled derate is standard practice and makes good maintenance cost control sense. However, I suspect that you miss the point. The intent is to save on hotend MTBF not become runway limited.
Could I ask you to enquire of your company's operations engineers what is their intent ? I should be enthralled to hear the answer. If it is to convert all takeoffs into runway limited exercises, then I shall studiously avoid flying with your company, as that philosophy augurs not well for the underlying risk management attitudes.
Of course you can convert a non-limiting takeoff into a limited example ... but who in his right mind would do so ? The majority of operators in my ken avoid going quite that far - and having been on the receiving end of the inquisitorial system, I suggest that that would be a difficult situation to argue convincingly at the coronial inquest with a couple of QCs breathing down your neck.
Operational scheduled derate is standard practice and makes good maintenance cost control sense. However, I suspect that you miss the point. The intent is to save on hotend MTBF not become runway limited.
Could I ask you to enquire of your company's operations engineers what is their intent ? I should be enthralled to hear the answer. If it is to convert all takeoffs into runway limited exercises, then I shall studiously avoid flying with your company, as that philosophy augurs not well for the underlying risk management attitudes.
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JT, a mute point but you are correct. We do reduce thrust take-offs to reduce strain on the engines and reduce maintenance costs. However, in doing so we end up utilising maximum runway length feasible (obviously we will not perform a 50% reduction take-off. Our airline has charts for max thrust, 10% and 20% reduced thrust take-offs however we refrain from using the 20% reduction.
In summary, the focal point is different but the result is the same.
In summary, the focal point is different but the result is the same.
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Moot points are just that but I would suggest that this is not an insignificant point at all. However, this probably is not the forum to pursue such matters of philosophy.
I am intrigued ... you suggest that you have derate to, as I recall, 55 percent or thereabouts. Why do you avoid a 20 percent derate? Are the charts printed on uninterestingly coloured paper ? Or is there some specific operations engineering or flight standards consideration ? What aircraft are we specifically discussing ?
I am intrigued ... you suggest that you have derate to, as I recall, 55 percent or thereabouts. Why do you avoid a 20 percent derate? Are the charts printed on uninterestingly coloured paper ? Or is there some specific operations engineering or flight standards consideration ? What aircraft are we specifically discussing ?
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John_Tullamarine,
We are basically a FAR-121 Flag carrier (non US based) and are usually considered conservative. The regulations permit us to reduce power by 25% of the rating in use. On Boeing aircraft we have the option of 3 takeoff ratings (Max, -10%, -20%), but we only use the 20% thrust reduction on the B747-400 to reduce VMCG on contaminated runways. We do not use it on other aircraft because neither the aircraft manufacturer or the engine manufacturer can quantify the benefits of doing so.
On the B777, Chapter 04 Performance was replaced by a computer program called AFM-DPI, there are no paper charts anymore. This program allows me to demonstrate how we use reduced thrust. (This isnt the format used by crews, they just see the normal Boeing multiple runway format, which are slightly more conservative that the AFM calculation)
Light Weight Actual Temperature.
Configuration
-------------
Model = 777-200 Brake Type = Cat A
Engine = GE90-90B Brake Config = All Operative
Thrust Derate = .0 Tire Speed = 235.00 MPH
Flaps = 5 Center of Gravity = Forward
Air Cond Bleed = On
Anti-ice Bleed = Off
Alternate Performance Level(s): Ten Minute Takeoff Thrust
Conditions
----------
Brake Release Gross Weight = 220000 KG
Certificate Limitations: Maximum Takeoff Weight = 286897 KG
Actual Temp = 15.0 DEG C
Assumed Temp = 15.0 DEG C
Pressure Altitude = 0 FEET
Runway Wind = 0 KNOTS
Runway Cond = Dry
TORA = 9000 FEET
TODA = 9000 FEET ASDA = 9000 FEET
Slope (Takeoff) = 1.00 PERCENT Slope (Accel-Stop) = 1.00 PERCENT
Takeoff Distances
-----------------
All Engine Takeoff Distance = 5569 FEET
All Engine Takeoff Run = 5084 FEET
One Engine Inoperative Takeoff Distance = 6112 FEET
One Engine Inoperative Takeoff Run = 5454 FEET
Accelerate-Stop Distance = 6112 FEET
Critical Distance(s) : One Engine Inop TO, Accel-Stop
The runway is 9000 feet long, so we convert that excess length into a power reduction, in this case using the 10% fixed derate and then finding the maximum assumed temperature.
Maximum Assumed Temperature Limit
---------------------------------
Field Length Limit 49.3 DEG C
Maximum Assumed Temperature Takeoff Distances
---------------------------------------------
All Engine Takeoff Distance = 8648 FEET
All Engine Takeoff Run = 8049 FEET
One Engine Inoperative Takeoff Distance = 8975 FEET
One Engine Inoperative Takeoff Run = 7935 FEET
Accelerate-Stop Distance = 8975 FEET
Critical Distance(s) : One Engine Inop TO, Accel-Stop
We are now using all the runway, as permitted by the FAR's and the AFM.
My understanding from Boeing Flight Ops Engineering people is that this is a common procedure amongst their operators, you obviously consider it dangerous, so please tell us what limit would you use?
If you dont agree with procedure, I guess that you dont agree with improved climb or the Airbus philosophy of optimized airspeeds either?
As for your intention ofstudiously avoid flying with your company , if we are considered "unsafe", you better get used to walking........
Mutt
We are basically a FAR-121 Flag carrier (non US based) and are usually considered conservative. The regulations permit us to reduce power by 25% of the rating in use. On Boeing aircraft we have the option of 3 takeoff ratings (Max, -10%, -20%), but we only use the 20% thrust reduction on the B747-400 to reduce VMCG on contaminated runways. We do not use it on other aircraft because neither the aircraft manufacturer or the engine manufacturer can quantify the benefits of doing so.
On the B777, Chapter 04 Performance was replaced by a computer program called AFM-DPI, there are no paper charts anymore. This program allows me to demonstrate how we use reduced thrust. (This isnt the format used by crews, they just see the normal Boeing multiple runway format, which are slightly more conservative that the AFM calculation)
Light Weight Actual Temperature.
Configuration
-------------
Model = 777-200 Brake Type = Cat A
Engine = GE90-90B Brake Config = All Operative
Thrust Derate = .0 Tire Speed = 235.00 MPH
Flaps = 5 Center of Gravity = Forward
Air Cond Bleed = On
Anti-ice Bleed = Off
Alternate Performance Level(s): Ten Minute Takeoff Thrust
Conditions
----------
Brake Release Gross Weight = 220000 KG
Certificate Limitations: Maximum Takeoff Weight = 286897 KG
Actual Temp = 15.0 DEG C
Assumed Temp = 15.0 DEG C
Pressure Altitude = 0 FEET
Runway Wind = 0 KNOTS
Runway Cond = Dry
TORA = 9000 FEET
TODA = 9000 FEET ASDA = 9000 FEET
Slope (Takeoff) = 1.00 PERCENT Slope (Accel-Stop) = 1.00 PERCENT
Takeoff Distances
-----------------
All Engine Takeoff Distance = 5569 FEET
All Engine Takeoff Run = 5084 FEET
One Engine Inoperative Takeoff Distance = 6112 FEET
One Engine Inoperative Takeoff Run = 5454 FEET
Accelerate-Stop Distance = 6112 FEET
Critical Distance(s) : One Engine Inop TO, Accel-Stop
The runway is 9000 feet long, so we convert that excess length into a power reduction, in this case using the 10% fixed derate and then finding the maximum assumed temperature.
Maximum Assumed Temperature Limit
---------------------------------
Field Length Limit 49.3 DEG C
Maximum Assumed Temperature Takeoff Distances
---------------------------------------------
All Engine Takeoff Distance = 8648 FEET
All Engine Takeoff Run = 8049 FEET
One Engine Inoperative Takeoff Distance = 8975 FEET
One Engine Inoperative Takeoff Run = 7935 FEET
Accelerate-Stop Distance = 8975 FEET
Critical Distance(s) : One Engine Inop TO, Accel-Stop
We are now using all the runway, as permitted by the FAR's and the AFM.
My understanding from Boeing Flight Ops Engineering people is that this is a common procedure amongst their operators, you obviously consider it dangerous, so please tell us what limit would you use?
If you dont agree with procedure, I guess that you dont agree with improved climb or the Airbus philosophy of optimized airspeeds either?
As for your intention ofstudiously avoid flying with your company , if we are considered "unsafe", you better get used to walking........
Mutt
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G'day mutt,
Could you please clarify.
Do the runway requirements you quote for a max Assumed Temp (49.3C) take off represent the actual lengths required if operating at an ACTUAL temperature of 49.3C at the given weight and conditions.
The reason I ask is that at an ACTUAL temperature of 15C there would be a considerable excess of performance versus the same take off at an ACTUAL 49.3c.
In other words we are "pretending" that it is 49.3C when it is actually 15C.
Could you please clarify.
Do the runway requirements you quote for a max Assumed Temp (49.3C) take off represent the actual lengths required if operating at an ACTUAL temperature of 49.3C at the given weight and conditions.
The reason I ask is that at an ACTUAL temperature of 15C there would be a considerable excess of performance versus the same take off at an ACTUAL 49.3c.
In other words we are "pretending" that it is 49.3C when it is actually 15C.
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Mutt,
Many thanks for taking the time to produce those sample figures - I have to say they do raise eyebrows amongst the pilot body.
Opinions on performance vary considerably depending on viewpoint. There seem to be three basic ones; commercial, Ops/Performance Engineering and the pilots actually strapped to the pointy object.
Now pilots genuinely do appreciate the commercial and safety benefits of reduced thrust/assumed temp. procedures. Destress the engine and thereby maintain its performance margins for longer and in turn extend life on the wing.
A significant number of us however do get very twitchy about taking it all the way to field length limitations. Here are some of the reasons why but first please be sure that this is not taking a personal poke at you or your colleagues. We're educating each other or at least passing on our differing perspectives.
As a professional you're taking data which you can only assume is proffered to you in good faith by the suppliers. You run the computations and come up with the figures. They have been factored for safety reasons to a level required by a controlling authority or agency.
A significant number of the readers of your post are horrified at the results. You have a professionally derived and, to you, entirely logical set of calculations which are legal and produce a a final safety net of 25 feet before going into the over-run, water or bundu.
Pilots take issue with this type of calculation on several counts.
The performance requirements are the result of down and dirty compromise between commercial interests and safety regulators. It is significant that many other authorities take a much more conservative stance than the FAA.
The performance figures have not been derived by real world pilots on normal commercial runways - they take no account of the oil and rubber residues completely coating the 600 to 200 metre section at the upwind end of the runway where we're trying to get max deceleration.
FDR and CVR analysis of real life problems and failures show the recognition and action time as certified is deeply flawed. Boeing effectively underline this with their papers on being Go minded.
The basic performance figures derived may not be glossy sales material for airshow goers but they are an utterly vital sales tool when dealing with the people who actually sign for the aircaft. Now, I'm sure this doesn't seem rational to you and your figures but the view we have ahead of us at V1 does not inspire us with confidence when field limited. Why?
Well, the data has been prepared without the extended turns and taxi times we have in the real world. The simple truth is this. The tyres will not hold out and even the best anti-skid unit in the world has a problem stopping on the wheel rims. Wild speculation? No!
A glance at the papers on the sites run by the tyre manufacturers clearly tell every one of us that when taxi times are greater than ten minutes all bets are off because of hysterysis in the sidewalls producing very high temperatures before we even begin the roll. Repeated turns have an even more deteterious effect. Yes, available brake energy may be factored in, tyre speed ratings as well but not the temperature and thus the integrity of our tyres when we begin the roll.
I hope we get the chance to discuss this over the long planned pint or two Mutt - but in the meantime I'd really like you to have a think about the points I've raised.
Performance Requirements created by all sides of industry.
Certification figures as a sales tool.
Reaction/action times close to V1
Rubber and oil Contaminated upwind braking areas
Tyre manufacturers disowning their products over extended (10 minutes!!)taxi times and turning prior to takeoff.
Please have a think about it, talk to your powerplant engineers about a cost/benefit analysis on derates versus deep derates. I think you'll find it's the first few percentage points of reduction that truly extend the engine margins - all else is willy waving to look good in meetings
Please give your guys a bit more concrete for the day they have to stop quite quickly. I'd be interested to see the the views of others on a 25 foot margin...........
Regards from the Towers
Rob Lloyd
[email protected]
[This message has been edited by PPRuNe Towers (edited 29 May 2001).]
Many thanks for taking the time to produce those sample figures - I have to say they do raise eyebrows amongst the pilot body.
Opinions on performance vary considerably depending on viewpoint. There seem to be three basic ones; commercial, Ops/Performance Engineering and the pilots actually strapped to the pointy object.
Now pilots genuinely do appreciate the commercial and safety benefits of reduced thrust/assumed temp. procedures. Destress the engine and thereby maintain its performance margins for longer and in turn extend life on the wing.
A significant number of us however do get very twitchy about taking it all the way to field length limitations. Here are some of the reasons why but first please be sure that this is not taking a personal poke at you or your colleagues. We're educating each other or at least passing on our differing perspectives.
As a professional you're taking data which you can only assume is proffered to you in good faith by the suppliers. You run the computations and come up with the figures. They have been factored for safety reasons to a level required by a controlling authority or agency.
A significant number of the readers of your post are horrified at the results. You have a professionally derived and, to you, entirely logical set of calculations which are legal and produce a a final safety net of 25 feet before going into the over-run, water or bundu.
Pilots take issue with this type of calculation on several counts.
The performance requirements are the result of down and dirty compromise between commercial interests and safety regulators. It is significant that many other authorities take a much more conservative stance than the FAA.
The performance figures have not been derived by real world pilots on normal commercial runways - they take no account of the oil and rubber residues completely coating the 600 to 200 metre section at the upwind end of the runway where we're trying to get max deceleration.
FDR and CVR analysis of real life problems and failures show the recognition and action time as certified is deeply flawed. Boeing effectively underline this with their papers on being Go minded.
The basic performance figures derived may not be glossy sales material for airshow goers but they are an utterly vital sales tool when dealing with the people who actually sign for the aircaft. Now, I'm sure this doesn't seem rational to you and your figures but the view we have ahead of us at V1 does not inspire us with confidence when field limited. Why?
Well, the data has been prepared without the extended turns and taxi times we have in the real world. The simple truth is this. The tyres will not hold out and even the best anti-skid unit in the world has a problem stopping on the wheel rims. Wild speculation? No!
A glance at the papers on the sites run by the tyre manufacturers clearly tell every one of us that when taxi times are greater than ten minutes all bets are off because of hysterysis in the sidewalls producing very high temperatures before we even begin the roll. Repeated turns have an even more deteterious effect. Yes, available brake energy may be factored in, tyre speed ratings as well but not the temperature and thus the integrity of our tyres when we begin the roll.
I hope we get the chance to discuss this over the long planned pint or two Mutt - but in the meantime I'd really like you to have a think about the points I've raised.
Performance Requirements created by all sides of industry.
Certification figures as a sales tool.
Reaction/action times close to V1
Rubber and oil Contaminated upwind braking areas
Tyre manufacturers disowning their products over extended (10 minutes!!)taxi times and turning prior to takeoff.
Please have a think about it, talk to your powerplant engineers about a cost/benefit analysis on derates versus deep derates. I think you'll find it's the first few percentage points of reduction that truly extend the engine margins - all else is willy waving to look good in meetings
Please give your guys a bit more concrete for the day they have to stop quite quickly. I'd be interested to see the the views of others on a 25 foot margin...........
Regards from the Towers
Rob Lloyd
[email protected]
[This message has been edited by PPRuNe Towers (edited 29 May 2001).]
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Posts: n/a
Morning Vicar,
One of the downfalls of modern technology is that its too accurate, the data shown above is "pretending that its 49.3°C when its actually 15°C", UNFORTUNATELY it is using that excess performance to get the required weight. If the ACTUAL: temperature was 49.3°C, the required runway would be
ERROR: Calculated accelerate-stop distance of 9112.5 FEET
is greater than the available stopping distance of 9000.0 FEET
(I'm not trying to be predantic by using 49.3° rather than 49°, this thing is so accurate that the 0.3° makes a 80 feet difference in the required distance)
To be cont........
Mutt.
One of the downfalls of modern technology is that its too accurate, the data shown above is "pretending that its 49.3°C when its actually 15°C", UNFORTUNATELY it is using that excess performance to get the required weight. If the ACTUAL: temperature was 49.3°C, the required runway would be
ERROR: Calculated accelerate-stop distance of 9112.5 FEET
is greater than the available stopping distance of 9000.0 FEET
(I'm not trying to be predantic by using 49.3° rather than 49°, this thing is so accurate that the 0.3° makes a 80 feet difference in the required distance)
To be cont........
Mutt.
Guest
Posts: n/a
Rob,
You may be sitting at the pointy end, but I'll probably be sitting right behind you, especially if its a Wednesday lunch time flight to London Therefore I have an immense personal interest in keeping both of us safe and getting to drink some Guinness
That 25 foot margin is a red herring, I could have just as easily ended up with ZERO.
We are probably the least commercial airline that you will ever find, we do not use the digital AFM as an operational tool, we use the more conservative standard Boeing takeoff charts. These charts dont know what your actual temperature is, therefore the calculation is based on ACTUAL temperatures. They do not account for the excess performance available due to the difference in TAS and available thrust. I will try to show this conservatism with the following.
I'm guessing that some of you are used to this kind of chart, for those that arent, you enter it at the bottom, read up until the you find your actual weight in both columns. In our case, it happens at 48°C and its field length limited.
ELEVATION 0 FT , ,MUTT INTL
***FLAPS 05*** ,PACKS ON ,
B777-200 ,GE90-DER I , ,DATED 29-MAY-2001
OAT, CLIMB, MAXIMUM ZERO WIND WEIGHT-(100 KG) AND LIMIT CODE
DEG C, LIMIT, , 14L
(I'm trying to save space, so there is a very limited range of temps)
45 , 2336, 2262F
46 , 2308, 2245F
47 , 2280, 2228F
48 , 2253, 2211F
49 , 2225, 2194F
50 , 2198, 2176F
67A, 1805, 1884F
68A, 1784, 1868F
69A, 1763, 1852F
ADD KG/KT HEADWIND 380
SUB KG/KT TAILWIND 1770
MIN FLAP RET HT-FT 800
RUNWAY LENGTH-FT 9006
RUNWAY SLOPE-PCT 1.00
CLEARWAY-FT 0
Now if the actual temperature was 48°C with 220,000 kgs, the actual takeoff performance would be as follows:
Takeoff Distances
-----------------
All Engine Takeoff Distance = 8580 FEET
All Engine Takeoff Run = 7983 FEET
One Engine Inoperative Takeoff Distance = 8909 FEET
One Engine Inoperative Takeoff Run = 7877 FEET
Accelerate-Stop Distance = 8909 FEET
Critical Distance(s) : One Engine Inop TO, Accel-Stop
That margin of 91 feet will increase as the actual temperature gets colder. For a 15°C day it would be 210 feet.
Remember that these stopping distances do not include the use of one thrust reverser.
Would you consider this margin to be sufficient? If not, how much would you like it to be?
Now to move on a bit, what accelerate stop margins do you expect when you are taking off at the ACTUAL temperature?
Mutt
You may be sitting at the pointy end, but I'll probably be sitting right behind you, especially if its a Wednesday lunch time flight to London
Therefore I have an immense personal interest in keeping both of us safe and getting to drink some Guinness That 25 foot margin is a red herring, I could have just as easily ended up with ZERO.
We are probably the least commercial airline that you will ever find, we do not use the digital AFM as an operational tool, we use the more conservative standard Boeing takeoff charts. These charts dont know what your actual temperature is, therefore the calculation is based on ACTUAL temperatures. They do not account for the excess performance available due to the difference in TAS and available thrust. I will try to show this conservatism with the following.
I'm guessing that some of you are used to this kind of chart, for those that arent, you enter it at the bottom, read up until the you find your actual weight in both columns. In our case, it happens at 48°C and its field length limited.
ELEVATION 0 FT , ,MUTT INTL
***FLAPS 05*** ,PACKS ON ,
B777-200 ,GE90-DER I , ,DATED 29-MAY-2001
OAT, CLIMB, MAXIMUM ZERO WIND WEIGHT-(100 KG) AND LIMIT CODE
DEG C, LIMIT, , 14L
(I'm trying to save space, so there is a very limited range of temps)
45 , 2336, 2262F
46 , 2308, 2245F
47 , 2280, 2228F
48 , 2253, 2211F
49 , 2225, 2194F
50 , 2198, 2176F
67A, 1805, 1884F
68A, 1784, 1868F
69A, 1763, 1852F
ADD KG/KT HEADWIND 380
SUB KG/KT TAILWIND 1770
MIN FLAP RET HT-FT 800
RUNWAY LENGTH-FT 9006
RUNWAY SLOPE-PCT 1.00
CLEARWAY-FT 0
Now if the actual temperature was 48°C with 220,000 kgs, the actual takeoff performance would be as follows:
Takeoff Distances
-----------------
All Engine Takeoff Distance = 8580 FEET
All Engine Takeoff Run = 7983 FEET
One Engine Inoperative Takeoff Distance = 8909 FEET
One Engine Inoperative Takeoff Run = 7877 FEET
Accelerate-Stop Distance = 8909 FEET
Critical Distance(s) : One Engine Inop TO, Accel-Stop
That margin of 91 feet will increase as the actual temperature gets colder. For a 15°C day it would be 210 feet.
Remember that these stopping distances do not include the use of one thrust reverser.
Would you consider this margin to be sufficient? If not, how much would you like it to be?
Now to move on a bit, what accelerate stop margins do you expect when you are taking off at the ACTUAL temperature?
Mutt
Join Date: Jan 1997
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Yep, your desire for a pint does see you strapping in alongside pilots on a very regular basis....
A very quick couple of points Mutt which I hope to edit later into a more cogent reply.
There shouldn't be any desire to see any margin at all as a result of your calculations. They should be seen as a perfectly valid, reasonable and acceptable. Real life says they are not for the reasons I gave earlier.
Just to provide a couple of further points to chew over:
If the performance rules and criteria are enlightened, accurate and honestly brokered why did it take 15 years of fighting in the alphabet soup groups and committees for there to be any allowance for the distance taken to enter, line up and straighten an aircraft on the runway?
Why was such a pathetic and measly distance, self-evidently required until Thunderbird 2 is employed to place aircraft at the very beginning of the TODA fought over so viciously?
Secondly the 210 feet real life/real temperature margin you come up with lends itself to some very basic mental arithmetic.
Switch that 210 feet from the safe, assured stop at the end of the runway to 210 feet around two thirds of the way down the take off run. Allied to the sort of speed your fleets will be bugging as V1 it comes at as something remarkably close to the extra second of decision/action time needed, used and reflected in the actual incident data so carefully recorded and preserved for us to learn from.
To sum up: Your data processing is elegant and accurate. However, pilot groups have now spent an entire generation trying to get the point across that the basic premise underlying these calculations are corrupt at the outset. The legal and technical framework is at fault not those who are tasked to produce our performance charts and calculations.
------------------
Regards from the Towers
[email protected]
A very quick couple of points Mutt which I hope to edit later into a more cogent reply.
There shouldn't be any desire to see any margin at all as a result of your calculations. They should be seen as a perfectly valid, reasonable and acceptable. Real life says they are not for the reasons I gave earlier.
Just to provide a couple of further points to chew over:
If the performance rules and criteria are enlightened, accurate and honestly brokered why did it take 15 years of fighting in the alphabet soup groups and committees for there to be any allowance for the distance taken to enter, line up and straighten an aircraft on the runway?
Why was such a pathetic and measly distance, self-evidently required until Thunderbird 2 is employed to place aircraft at the very beginning of the TODA fought over so viciously?
Secondly the 210 feet real life/real temperature margin you come up with lends itself to some very basic mental arithmetic.
Switch that 210 feet from the safe, assured stop at the end of the runway to 210 feet around two thirds of the way down the take off run. Allied to the sort of speed your fleets will be bugging as V1 it comes at as something remarkably close to the extra second of decision/action time needed, used and reflected in the actual incident data so carefully recorded and preserved for us to learn from.
To sum up: Your data processing is elegant and accurate. However, pilot groups have now spent an entire generation trying to get the point across that the basic premise underlying these calculations are corrupt at the outset. The legal and technical framework is at fault not those who are tasked to produce our performance charts and calculations.
------------------
Regards from the Towers
[email protected]
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Mutt,
Thanks mate. Meaty stuff.
I don't suggest that using whatever level of derate a particular operator chooses necessarily is dangerous at all - except when the calculated accel stop is made limiting - that is really walking a razorblade for the subsequent enquiry. The observations made by Rob Lloyd I echo with vigour.
I presume that you are an ops engineer, and no doubt very competent in the technical aspects of the job, but not a line pilot. I can relate to that sort of scenario. I went to a line flying job from such a background, and I must confess that I did so .... thinking that I knew it all.... ah .. the heady brashness of youth.
The first takeoff in that wonderful F27 machine (after I had finally developed big leg muscles and worked out how to stay right way up) .. on a limiting runway .. with V1 occuring, as I recall, sometime after I lost sight of the far end of the runway ... established quite clearly in my mind .. that I knew SFA... and put the wind up me in no uncertain terms. In biblical style, I had a revelation .. and became very, very much more conservatively critical in my engineering work.
But the simple fact (to which Rob Lloyd alludes) is that engineers philosophically think very differently to pilots (and engineer-pilots are, of course, never quite sure what they are thinking). The sums are wonderful and the manufacturer's Fortran programs can give answers to the nth decimal place. The real world, however, is a nasty, dirty place in which the sums are only a valiant effort to describe what really happens. He who believes the sums .. without a pragmatic dose of cynical reality ... slides on a slippery slope. The same sort of thought applies to glass ships .. he who doesn't keep an eye on the raw data .. does likewise.
My real concern relates to a prudent risk averse philosophy in that .. why would one trade all the fortuitous gain of a long runway when a comfort margin might be maintained without significant loss of the derate benefit ? Of course, that becomes less flexible if you only use discrete thrust derate margins.
Quite clearly, each operator has to make an appropriate assessment against its own operational and corporate risk management philosophies.
Following on from the preceding, my comment regarding "after the event" inquisitions is, I suggest, very pertinent.
Most aviation people have never been subjected to legal inquisition - and the experience is far from being a pleasant one.
I suggest that an operator is much better placed to defend a derate procedure if it is not taken to the nth degree in an aspect so fraught with variability as the accel stop - there are just too many minor imponderables in the real world application of the sums - runway longitudinal profile, touchdown zone contaminants, and actual "on-the-runway" OAT versus tower temperature on a nice clear summer's day come to mind, for example.
In essence, the AFM really isn't about guarantees - it provides reference data only .. in the nature of "in these conditions, and under these circumstances, if you do such and such, then you can expect to get some quantifiable, and probably repeatable, outcome".
That has not a lot to do with the real world of routine operations under limiting conditions.
Am I cautious ? You bet I am. Do I accept the commercial and corporate realities ? Of course I do. It comes down to a matter of balancing the accountant's desire for profit against the pilot's desire not to die.
In practical terms, it is these sorts of variable things that the QCs will leap upon with great relish to push their particular client's barrow - at your expense - and often quite literally.
I recall an accident that did major damage to two air carrier machines (and was so very nearly a disaster in a similar style to the Teneriffe catastrophe) in one of the Antipodean countries quite some years ago. One crew, which could see the problem unfolding, and having done what most of us would have considered a pretty reasonable sort of job, were castigated by the investigation for not having 20/20 ops eng mathematical hindsight ahead of the foresight - and have we not heard this sort of thing from time to time in accident investigations ?
As I recall, in the ensuing litigation, the captain was assigned 33 percent of the blame and costs - now ... is that, or is that not, a sobering thought ?
To your other comments -
I am all for overspeed V2 operations when the runway/obstacle profiles dictate.
I am not familiar with the Airbus procedure - perhaps you could provide a quick summary for those of us who have not played with that particular manufacturer's toys.
As for my gratuitous comment regarding not travelling with your airline, that was intended as a tongue-in-cheek impertinent remark - sorry if I needlessly lit your wick a bit there ....
My suggested limit for derate - very simple - is the intended climb thrust setting.
Thinking back to one of the ops engineers who did a lot of the early work on derate takeoffs in the 60s with a longhaul operator, he told a lovely tale of the early work on 707s when a story came back from the line that the pilots, on one occasion, were somewhat nonplussed sometime after liftoff ... by the FE's advancing the throttles on the call for climb thrust.
As that seemed quite a reasonable concern, the procedure was amended to restrict the derate to climb thrust settings.
His derate philosophy, as best I can recall, also included a proviso that the accel stop was never to be more limiting than a 1000 ft pad. But, then again, he had an operational flying background.
[This message has been edited by john_tullamarine (edited 29 May 2001).]
Thanks mate. Meaty stuff.
I don't suggest that using whatever level of derate a particular operator chooses necessarily is dangerous at all - except when the calculated accel stop is made limiting - that is really walking a razorblade for the subsequent enquiry. The observations made by Rob Lloyd I echo with vigour.
I presume that you are an ops engineer, and no doubt very competent in the technical aspects of the job, but not a line pilot. I can relate to that sort of scenario. I went to a line flying job from such a background, and I must confess that I did so .... thinking that I knew it all.... ah .. the heady brashness of youth.
The first takeoff in that wonderful F27 machine (after I had finally developed big leg muscles and worked out how to stay right way up) .. on a limiting runway .. with V1 occuring, as I recall, sometime after I lost sight of the far end of the runway ... established quite clearly in my mind .. that I knew SFA... and put the wind up me in no uncertain terms. In biblical style, I had a revelation .. and became very, very much more conservatively critical in my engineering work.
But the simple fact (to which Rob Lloyd alludes) is that engineers philosophically think very differently to pilots (and engineer-pilots are, of course, never quite sure what they are thinking). The sums are wonderful and the manufacturer's Fortran programs can give answers to the nth decimal place. The real world, however, is a nasty, dirty place in which the sums are only a valiant effort to describe what really happens. He who believes the sums .. without a pragmatic dose of cynical reality ... slides on a slippery slope. The same sort of thought applies to glass ships .. he who doesn't keep an eye on the raw data .. does likewise.
My real concern relates to a prudent risk averse philosophy in that .. why would one trade all the fortuitous gain of a long runway when a comfort margin might be maintained without significant loss of the derate benefit ? Of course, that becomes less flexible if you only use discrete thrust derate margins.
Quite clearly, each operator has to make an appropriate assessment against its own operational and corporate risk management philosophies.
Following on from the preceding, my comment regarding "after the event" inquisitions is, I suggest, very pertinent.
Most aviation people have never been subjected to legal inquisition - and the experience is far from being a pleasant one.
I suggest that an operator is much better placed to defend a derate procedure if it is not taken to the nth degree in an aspect so fraught with variability as the accel stop - there are just too many minor imponderables in the real world application of the sums - runway longitudinal profile, touchdown zone contaminants, and actual "on-the-runway" OAT versus tower temperature on a nice clear summer's day come to mind, for example.
In essence, the AFM really isn't about guarantees - it provides reference data only .. in the nature of "in these conditions, and under these circumstances, if you do such and such, then you can expect to get some quantifiable, and probably repeatable, outcome".
That has not a lot to do with the real world of routine operations under limiting conditions.
Am I cautious ? You bet I am. Do I accept the commercial and corporate realities ? Of course I do. It comes down to a matter of balancing the accountant's desire for profit against the pilot's desire not to die.
In practical terms, it is these sorts of variable things that the QCs will leap upon with great relish to push their particular client's barrow - at your expense - and often quite literally.
I recall an accident that did major damage to two air carrier machines (and was so very nearly a disaster in a similar style to the Teneriffe catastrophe) in one of the Antipodean countries quite some years ago. One crew, which could see the problem unfolding, and having done what most of us would have considered a pretty reasonable sort of job, were castigated by the investigation for not having 20/20 ops eng mathematical hindsight ahead of the foresight - and have we not heard this sort of thing from time to time in accident investigations ?
As I recall, in the ensuing litigation, the captain was assigned 33 percent of the blame and costs - now ... is that, or is that not, a sobering thought ?
To your other comments -
I am all for overspeed V2 operations when the runway/obstacle profiles dictate.
I am not familiar with the Airbus procedure - perhaps you could provide a quick summary for those of us who have not played with that particular manufacturer's toys.
As for my gratuitous comment regarding not travelling with your airline, that was intended as a tongue-in-cheek impertinent remark - sorry if I needlessly lit your wick a bit there ....
My suggested limit for derate - very simple - is the intended climb thrust setting.
Thinking back to one of the ops engineers who did a lot of the early work on derate takeoffs in the 60s with a longhaul operator, he told a lovely tale of the early work on 707s when a story came back from the line that the pilots, on one occasion, were somewhat nonplussed sometime after liftoff ... by the FE's advancing the throttles on the call for climb thrust.
As that seemed quite a reasonable concern, the procedure was amended to restrict the derate to climb thrust settings.
His derate philosophy, as best I can recall, also included a proviso that the accel stop was never to be more limiting than a 1000 ft pad. But, then again, he had an operational flying background.
[This message has been edited by john_tullamarine (edited 29 May 2001).]
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Mutt--
I worked for the same carrier for a long time (all on the L1011) and when these aircraft were new, maximum engine derate, to 54C, was used when able. I left some years ago and wonder if this same derate was used as the airplanes had been bashed around a lot. The maximum derate works very well when the engines are new, how about when they (and the airframe) are old and tired?
I worked for the same carrier for a long time (all on the L1011) and when these aircraft were new, maximum engine derate, to 54C, was used when able. I left some years ago and wonder if this same derate was used as the airplanes had been bashed around a lot. The maximum derate works very well when the engines are new, how about when they (and the airframe) are old and tired?
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My post was not clear I am sorry. I meant the difference between actual and the FAR 25 requirement for 115% of Balance Field length is around 600-700 ft. The difference between standing start and rolling is greater than 50 FT unless you roll around the corner at 40 mph and start spoolup, but try it in a 747 and you might end up in the grass. Its going to depend a lot on altitude and temp and all the other stuff that goes into low speed performance.
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I'm going for the easy one first.......
411A, you were here when the L1011's were NEW????? I think that I was still in diapers. Anway the assumed thrust procedures remained the same until the aircraft were retired. Due to the environment and the route structure, it was the only way of keeping the RB211's on the wings. Its only the newer Seattle built Boeings that have increased the temperature band to 69C. Obviously between 54C and 69C can only be used for assumed thrust and not as an extended environmental envelope.
All the best.
Mutt
411A, you were here when the L1011's were NEW????? I think that I was still in diapers. Anway the assumed thrust procedures remained the same until the aircraft were retired. Due to the environment and the route structure, it was the only way of keeping the RB211's on the wings. Its only the newer Seattle built Boeings that have increased the temperature band to 69C. Obviously between 54C and 69C can only be used for assumed thrust and not as an extended environmental envelope.
All the best.
Mutt