Overweight Landing and Field Length
Join Date: Sep 1998
Location: wherever
Age: 55
Posts: 1,616
Likes: 0
Received 0 Likes
on
0 Posts
Haroon,
It's just a bit of maths.
You need to land in 60% of the available distance. That means you must have 1/60x100 of your actual landing distance available. That's the same as 1.66 recurring so 1.67 is used.
For a wet runway we must have 115% of the dry figure so we could do two calculations or we could simply calculate 1.92 X actual landing distance.
For a test pilot actual landing distance = unfactored landing distance. And in many companies this is what is used for line operations.
It could be argued that as we know the average line pilot is not likely to meet the test pilots results we should use more to fully comply with the spirit of the law but you wont find many(any!) operations that include a line pilot factor.
It's just a bit of maths.
You need to land in 60% of the available distance. That means you must have 1/60x100 of your actual landing distance available. That's the same as 1.66 recurring so 1.67 is used.
For a wet runway we must have 115% of the dry figure so we could do two calculations or we could simply calculate 1.92 X actual landing distance.
For a test pilot actual landing distance = unfactored landing distance. And in many companies this is what is used for line operations.
It could be argued that as we know the average line pilot is not likely to meet the test pilots results we should use more to fully comply with the spirit of the law but you wont find many(any!) operations that include a line pilot factor.
Join Date: May 2000
Location: Seattle
Posts: 3,195
Likes: 0
Received 0 Likes
on
0 Posts
Inverting the safety factor numbers may be "just a bit of maths," but it serves to confuse more than anything else. In these forums, using the numbers actually cited in the various regulations would be a much better idea...
Problem with the various regulations is they are not consistent themselves. Aviation is a profession with a few numbers - a bit of simple maths shouldn't be beyond anyone here! 
Aviation safety requires avoidance of unnecessary risk; risk depends on the hazard, frequency of encounter (likelihood), and the severity of the consequences. The process (risk assessment) requires judgment, which in turn requires dependable knowledge and appropriate skills of thought.
A safety factor provides a buffer between the hazard and the planned operation. It is a margin for ‘error’ or deviation from the ideal to minimize the risk(s) and/or alleviate consequences of the hazard.
Haroon discusses ’ the ‘ safety factor (#34), but the issue is ’ a ‘ safety factor, relating to a specific situation and the assumptions made about human behavior/capability (in that situation). Hence, in an emergency (change of situation), the landing-distance safety-factor can be reduced. Note that although a wet landing uses a landing–distance factor of 1.92 it is not necessarily the same safety factor as for a dry runway as the increasing number of the accidents indicates.
Thus, the debate is firstly whether the event is an emergency or not – it’s not; and secondly if an over weight landing were to be attempted what distance is required to provide a margin of safety equivalent to a max wt landing on a dry runway.
EU-OPS 1.475 requires a 1.67 factor (normal operation – in flight replanning).
The QRH actual landing distance (5700ft) is probably shorter than the certificated actual landing distance because reverse detent is used (I assume that this is idle, vice ‘max reverse’ quoted elsewhere in the QRH).
Thus by adding 220ft (QRH adjustment for no reverse), the certificated actual (overweight) distance is ~ 6000ft.
A 1.67 factor would require ~ 10,000ft runway.
However, this calculation does not consider other / new risks such as brake energy limit, brake fade, landing gear limits (vertical rate and side loads).
As all risk assessments should be specific to the situation, the calculations for the overweight landing above does not use an equivalent basis as a for max wt landing, and it is these differences which might sway the argument for not landing overweight without an emergency as the aircraft is not certificated for this on a regular basis.
Re The flight safety foundation have a good briefing. (F E Hoppy), is this the one? http://www.skybrary.aero/bookshelf/books/874.ppt
A recent FSF report outlines the nature of the risks, but provides few practical remedies - http://www.skybrary.aero/bookshelf/books/900.pdf
A similar but more practical document is ‘Runway excursions’ by ASTB.
For some ‘How To’ aspects – Judgement etc see Aviation.org, - ‘library’ section, presentations on Critical Thinking, Situation Awareness, and Decision Making (free registration required).
A safety factor provides a buffer between the hazard and the planned operation. It is a margin for ‘error’ or deviation from the ideal to minimize the risk(s) and/or alleviate consequences of the hazard.
Haroon discusses ’ the ‘ safety factor (#34), but the issue is ’ a ‘ safety factor, relating to a specific situation and the assumptions made about human behavior/capability (in that situation). Hence, in an emergency (change of situation), the landing-distance safety-factor can be reduced. Note that although a wet landing uses a landing–distance factor of 1.92 it is not necessarily the same safety factor as for a dry runway as the increasing number of the accidents indicates.
Thus, the debate is firstly whether the event is an emergency or not – it’s not; and secondly if an over weight landing were to be attempted what distance is required to provide a margin of safety equivalent to a max wt landing on a dry runway.
EU-OPS 1.475 requires a 1.67 factor (normal operation – in flight replanning).
The QRH actual landing distance (5700ft) is probably shorter than the certificated actual landing distance because reverse detent is used (I assume that this is idle, vice ‘max reverse’ quoted elsewhere in the QRH).
Thus by adding 220ft (QRH adjustment for no reverse), the certificated actual (overweight) distance is ~ 6000ft.
A 1.67 factor would require ~ 10,000ft runway.
However, this calculation does not consider other / new risks such as brake energy limit, brake fade, landing gear limits (vertical rate and side loads).
As all risk assessments should be specific to the situation, the calculations for the overweight landing above does not use an equivalent basis as a for max wt landing, and it is these differences which might sway the argument for not landing overweight without an emergency as the aircraft is not certificated for this on a regular basis.
Re The flight safety foundation have a good briefing. (F E Hoppy), is this the one? http://www.skybrary.aero/bookshelf/books/874.ppt
A recent FSF report outlines the nature of the risks, but provides few practical remedies - http://www.skybrary.aero/bookshelf/books/900.pdf
A similar but more practical document is ‘Runway excursions’ by ASTB.
For some ‘How To’ aspects – Judgement etc see Aviation.org, - ‘library’ section, presentations on Critical Thinking, Situation Awareness, and Decision Making (free registration required).
Join Date: Sep 1998
Location: wherever
Age: 55
Posts: 1,616
Likes: 0
Received 0 Likes
on
0 Posts
Safetypee,
I was refering to this:
Approach and Landing Accident Reduction (ALAR) | Flight Safety Foundation
Well worth reading through the whole thing for those with a little time to spare. Section 8 is most pertinent to this discussion.
I was refering to this:
Approach and Landing Accident Reduction (ALAR) | Flight Safety Foundation
Well worth reading through the whole thing for those with a little time to spare. Section 8 is most pertinent to this discussion.
Thread Starter
Join Date: Nov 2009
Location: PK
Posts: 195
Likes: 0
Received 0 Likes
on
0 Posts
Hello again. Sorry for the late response as I got stuck in a busy pattern after the sim.
FE Hoppy thanx for the reference I was looking for. Perhaps I did'nt pay proper attention to the terminologies used i.e "Margin" and "Factor" in my last post.
If I have understood correctly now then to land within 60% of the landing distance available means 40% of the landing distance available will be there for us as a safety margin.
i.e. If landing distance avaialble is 10,000 feet then aircraft has to stop
within 6000 feet so that the remaining 4000 feet is avaialable as a
safety margin. The remaining 4000 feet is 40% safety margin in
reference to landing distance available and 67% safety margin in
reference to landing distance in which the aircraft stops.
Thus in reference to the aircraft actual landing performance
Margin of Safety = 67%
Safety Factor = 1.67
Whereas in reference to landing distance avaialble the margin of safety = 40%
Thankyou all
FE Hoppy thanx for the reference I was looking for. Perhaps I did'nt pay proper attention to the terminologies used i.e "Margin" and "Factor" in my last post.
If I have understood correctly now then to land within 60% of the landing distance available means 40% of the landing distance available will be there for us as a safety margin.
i.e. If landing distance avaialble is 10,000 feet then aircraft has to stop
within 6000 feet so that the remaining 4000 feet is avaialable as a
safety margin. The remaining 4000 feet is 40% safety margin in
reference to landing distance available and 67% safety margin in
reference to landing distance in which the aircraft stops.
Thus in reference to the aircraft actual landing performance
Margin of Safety = 67%
Safety Factor = 1.67
Whereas in reference to landing distance avaialble the margin of safety = 40%
Thankyou all
Join Date: Nov 2001
Location: S51 30 W060 10.
Posts: 197
Likes: 0
Received 0 Likes
on
0 Posts
if pax are calm, and no one is hurt, i would hold and land within max landing wt, course I'd check wx, talk to the company and everything, but I wouldn´t land a 737 or a 320 with 7 tons overwt, at night, out of a non precision approach, JUST to save fuel. Again if there´s one good reason to land overwt, eg a pax not feeling well, weather deteriorating really bad, I´d think about terminating the flight, otherwise I´d burn off fuel.
Join Date: Jan 2001
Location: Australia
Posts: 725
Likes: 0
Received 0 Likes
on
0 Posts
A very interesting thread, and a worthy Techlog discussion 
I cannot add much more in the way of wisdom, but perhaps can help simplify it or provide a 'take-away' point.
1. Decision maker's rule of thumb for attempting an Overweight (over MLW) landing:
"Is the hazard of continued flight, greater than the hazards of an overweight landing?"
The hazards of the overweight landing having been identified by FE Hoppy, JT and others. Especially the exponential increase in energy that must be absorbed by the gear and airframe on touchdown (Vg Max) and then dissipated via braking systems. Also, beware the temptation to overestimate one's capabilities to 'handle' an abnormal situation.
If you can't dump the fuel, and nobody is likely to die or be injured by your holding 1hr or 2 hrs -- hold.
2. "Make fuel on the easy days. Not the tough days."
If your airline is like our airline, the focus on reducing carriage of 'discretionary' fuel and routinely uplifting Minimum Operational Requirement across the network, every day, will have more than offset your burning 4 (or 20) tonnes the one day you may be called to do that.
3. Overweight landings are different from 'not full factors' landings.
You may also be faced with the situation where you are at or below structural MLW, but forced to consider putting your aeroplane into a field that does not meet the 'full factors' 1.67 (dry) or 1.92 (wet).
In that case, you have eliminated one unknown - you will have landed your aircraft at that weight many times before. You are in familiar territory, handling-wise.
But halving the factor, is quartering the margin for error.
If, after considering the italicised advice, you need to put your aircraft onto a runway that has less than full factors, you have a situation that your cabin crew, your pax, and the airfield services ought to be briefed in on. The subsequent landing will not be pretty, braking may be forceful, and any handling error on your part might have you off the fairway and in the rough. Literally.
My 2c worth.
Great discussion.
I cannot add much more in the way of wisdom, but perhaps can help simplify it or provide a 'take-away' point.
1. Decision maker's rule of thumb for attempting an Overweight (over MLW) landing:
"Is the hazard of continued flight, greater than the hazards of an overweight landing?"
The hazards of the overweight landing having been identified by FE Hoppy, JT and others. Especially the exponential increase in energy that must be absorbed by the gear and airframe on touchdown (Vg Max) and then dissipated via braking systems. Also, beware the temptation to overestimate one's capabilities to 'handle' an abnormal situation.
If you can't dump the fuel, and nobody is likely to die or be injured by your holding 1hr or 2 hrs -- hold.
2. "Make fuel on the easy days. Not the tough days."
If your airline is like our airline, the focus on reducing carriage of 'discretionary' fuel and routinely uplifting Minimum Operational Requirement across the network, every day, will have more than offset your burning 4 (or 20) tonnes the one day you may be called to do that.
3. Overweight landings are different from 'not full factors' landings.
You may also be faced with the situation where you are at or below structural MLW, but forced to consider putting your aeroplane into a field that does not meet the 'full factors' 1.67 (dry) or 1.92 (wet).
In that case, you have eliminated one unknown - you will have landed your aircraft at that weight many times before. You are in familiar territory, handling-wise.
But halving the factor, is quartering the margin for error.
If, after considering the italicised advice, you need to put your aircraft onto a runway that has less than full factors, you have a situation that your cabin crew, your pax, and the airfield services ought to be briefed in on. The subsequent landing will not be pretty, braking may be forceful, and any handling error on your part might have you off the fairway and in the rough. Literally.
My 2c worth.
Great discussion.
Last edited by ITCZ; 4th Dec 2009 at 15:23.
Join Date: Oct 2006
Location: Europe
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Overweigh Landing extremely simple
Dear all
An overweight landing assumes there is no time for dumping or dumping is not possible.
There is no regulation that requires factoring.
As a guideline: runway, climb and obstacles limitations need to de taken into account.
Overweight combines adversely with any system failures that affect deceleration and/or controlability.
Piece of cake.
An overweight landing assumes there is no time for dumping or dumping is not possible.
There is no regulation that requires factoring.
As a guideline: runway, climb and obstacles limitations need to de taken into account.
Overweight combines adversely with any system failures that affect deceleration and/or controlability.
Piece of cake.
Join Date: Jan 2001
Location: Australia
Posts: 725
Likes: 0
Received 0 Likes
on
0 Posts
There is no regulation that requires factoring.
Would you fly with 0% variable and 0 minutes fixed fuel reserves, if there were no regulation? What would guide you in your decision on fuel reserve, if there were no regulation?
We still have a duty of care. We all know that we are not all test pilots flying in controlled test conditions. We know that, and the court of inquiry will know that too.
How do you assess it, if not by reference to factors implied by regulations as being a suitable standard?
Do you use another method? One that can stand scrutiny?
I ask out of curiosity, not rhetorically - factors are treated as in-flight requirements as well as pre-departure requirement over here.
Join Date: Oct 2006
Location: Europe
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Its up to the sound judgement of the captan.
And yes I do have some good guidelines that have been found sound by various chief pilots of mayor flag carriers.
Ask Emirates Airlines it they can stand up that challenge.
And yes I do have some good guidelines that have been found sound by various chief pilots of mayor flag carriers.
Ask Emirates Airlines it they can stand up that challenge.
Last edited by Pitch Up Authority; 4th Dec 2009 at 16:32.
Join Date: Oct 2006
Location: Europe
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
ITCZ: Its not a game.
You will find out the day you ever have to take a serious decision. My post regarding overweight landing is correct and reflects the current state of rules and regulations.
Any margin that a company wants to build in is at their own discretion and policy.
You referred in your post to a possible court investigation if something would ever go wrong, I thank you for that remark. I hope you are able to asses that implication wisely and pass it on to whoever you fly with.
I took the decision to share the extend my experience with whom I like and there is nothing wrong with that.
By the way I even have a method that makes your decision completely independent of braking action and malfunctions in the brake system but not for you.
ITCZ: Thank you for the PM. If you claim to have 24000 hrs and be a Chief Pilot it should be easy for you to put in cristal clear language your vieuws and policies regarding overweight landings. I hope I can learn something from it but at a certain moment the learning stops and the teaching starts
You will find out the day you ever have to take a serious decision. My post regarding overweight landing is correct and reflects the current state of rules and regulations.
Any margin that a company wants to build in is at their own discretion and policy.
You referred in your post to a possible court investigation if something would ever go wrong, I thank you for that remark. I hope you are able to asses that implication wisely and pass it on to whoever you fly with.
I took the decision to share the extend my experience with whom I like and there is nothing wrong with that.
By the way I even have a method that makes your decision completely independent of braking action and malfunctions in the brake system but not for you.
ITCZ: Thank you for the PM. If you claim to have 24000 hrs and be a Chief Pilot it should be easy for you to put in cristal clear language your vieuws and policies regarding overweight landings. I hope I can learn something from it but at a certain moment the learning stops and the teaching starts
Last edited by Pitch Up Authority; 4th Dec 2009 at 19:24.
Thread Starter
Join Date: Nov 2009
Location: PK
Posts: 195
Likes: 0
Received 0 Likes
on
0 Posts
Thankyou SuddenWinds, ITCZ and Pitch Up Authority for your posts.
Pitch Up Authority:
You mentioned that,
But the company minima cannot be below the regulatory minima, please correct me if I am wrong.
Secondly you mentioned that,
But as pointed out by FE Hoppy earlier in this discussion JAR OPS 1.475 and 1.515 states the regulation which requires this factoring for in flight re-planning (if there is no emergency).
Though I am not a test pilot but I am optimistic that I would be able to land within the landing distance available in conditions which are mentioned in this post. I believe even those who say they wont land in these conditions are able to do so.
But we are not optimistic about the fact that absolutely nothing can go wrong. It is very much possible to enter the Caution Zone after landing (if nothing else goes wrong) and if a tire deflates and one is unable to vacate the runway then is there something that will protect us from the legal side
especially when the regulation does not allow us to land unfactored.
Things can go wrong even after full compliance with the regulations but at least we are legally covered. So basically at this point of discussion we are trying to focus more on the legal side because we need protection on that end apart from passenger and flight safety.
Pitch Up Authority:
You mentioned that,
Any margin that a company wants to build in is at their own discretion and policy
Secondly you mentioned that,
There is no regulation that requires factoring
Though I am not a test pilot but I am optimistic that I would be able to land within the landing distance available in conditions which are mentioned in this post. I believe even those who say they wont land in these conditions are able to do so.
But we are not optimistic about the fact that absolutely nothing can go wrong. It is very much possible to enter the Caution Zone after landing (if nothing else goes wrong) and if a tire deflates and one is unable to vacate the runway then is there something that will protect us from the legal side
especially when the regulation does not allow us to land unfactored.Things can go wrong even after full compliance with the regulations but at least we are legally covered. So basically at this point of discussion we are trying to focus more on the legal side because we need protection on that end apart from passenger and flight safety.
Join Date: Oct 2006
Location: Europe
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Its about our own Safety NOT that of the passengers
One of the shortcommings in ATPL courses is that there is not enough atttention for the background and reasoning behind certain rules, regulations and limitations. (ex Crosswind limitations, validity of friction coeficients etc....)
It looks like these gaps are sometimes covered by operator trainig programs and manufacturers efforts to inform pilots more than they have done in the past. Technical commisions within pilot unions try to do the same but these organisations have often very limited resources.
Individuals that were and are member of ICAO and JAA performance comities have addressed certain topics but have also highlighted some of the shortcomings of the regulatory proces.
There are a few things we can do but this is not the place.
In the end its about our own safety, nobody can ever accuse you of putting the safety of your pax at danger except a corrupt system.
It looks like these gaps are sometimes covered by operator trainig programs and manufacturers efforts to inform pilots more than they have done in the past. Technical commisions within pilot unions try to do the same but these organisations have often very limited resources.
Individuals that were and are member of ICAO and JAA performance comities have addressed certain topics but have also highlighted some of the shortcomings of the regulatory proces.
There are a few things we can do but this is not the place.
In the end its about our own safety, nobody can ever accuse you of putting the safety of your pax at danger except a corrupt system.
Last edited by Pitch Up Authority; 6th Dec 2009 at 21:13.
Thread Starter
Join Date: Nov 2009
Location: PK
Posts: 195
Likes: 0
Received 0 Likes
on
0 Posts
One of the shortcommings in ATPL courses is that there is not enough atttention for the background and reasoning behind certain rules, regulations and limitations.
Individuals that were and are member of ICAO and JAA performance comities have addressed certain topics but have also highlighted some of the shortcomings of the regulatory proces.
In the end its about our own safety, nobody can ever accuse you of putting the safety of your pax at danger except a corrupt system.
Join Date: Oct 2006
Location: Europe
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Its good to know the background but once a regulation is made it has to be followed regardless of the reasoning behind it. I mean if a policeman catches me on crossing a red light, I cant argue that I should not be punished on the basis that I didn't bang into any other car, as collision avoidance was the main reason of traffic lights at a crossing.
There are shortcomings because regulations are made by humans and one cannot rule out human factors/limitaions. But to challenge a regulation one has to submit evidence against it to the concerned committee so that a revision is issued. Until the new regulation is issued the previous one remains valid in the court of law.
Legal Implications + Corrupt System = Nightmare
During normal operations I used to (were possible) decelerate with reversers only. After a while you get a fairly accurate idea what lenght you need as function of touch down ground speed. This method makes you independent of brake system problems and breaking action. The only problem is the reliability of the reversers as function of system reliability and the combination of braking action/ crosswind.
It puts the advisory data for slippery runways in another context. These data are subject to fierce discussions at all levels. Directional control problems as a consequence of uneven braking being one of them.
Basicaly you can always land on the runway to took off from if it is dry. Max brake energy may be a limitation.
If it is not dry you better look carefully at groundspeed on touchdown and slope when you choose your RWY. This becomes more important on slippery runways. Those who live in the northern part of our globe know all about this.
Last edited by Pitch Up Authority; 10th Dec 2009 at 10:27.