Actual Landing Distance WET - how is it determined?
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When deciding on company policy we look at what is achievable by an average pilot, we therefore do not consider the "actual landing" distances as usable unless they are factored or its an emergency.
Maybe we are just unique
Maybe we are just unique
In this context actual landing distances are only used in case of landing with technical abnormals or emergencies. For dispatching, operating and even diverting in flight Required Distances are considered.
As out Flight Safety Department is just starting a major campaign 'Avoiding ALAs' I recently saw some very interesting statistics from our Flight Data Monitoring, where Required Landings Distances were compared to the distances achieved in our daily ops. Operating in 'limiting' airfields, maybe under adverse conditions, using Actual LDs sounds like an accident waiting to happen. At least with an FBW-Airbus.
I drove the BAe-RJ85 before, so I guess I can say I saw a lot of landings into 'limiting' airports like LCY or FLR. However I personally rate the braking capability of the RJ (which even hasn't Reverse) much better than the A319-A320. AZ (or was it Meridiana) operating with A319s into FLR, wouldn't do it
Still by talking to colleagues of other airlines who are operating to JAR-OPS+0, I wonder quite often how many ways JAR-OPS offers to bring yourself into trouble perfeclty legal.
Nothing beats success - What's the other side of the medail?
Regards, MAX
It may be just one of those days, (multitasking or I’m just below average), but I don’t follow all of the reasoning in accepting a 3120m actual landing distance on a 3300m runway without explanation of the assumption. As discussed extensively above, the industry accepts a 1.97 ‘factor’ (1.67x1.15) on top of the actual dry landing distance. ‘Accepts’ is used in the sense that this does not necessarily provide the same margin of safety when landing on a dry runway with a factor of 1.67, but it is equivalent (“equal, all things considered”) i.e. satisfactory for a range of normal operations provided the relevant ‘things’ are considered.
So why should we accept a significant reduction in safety margin in the use of 3120m as opposed to the fully factored distance? Is this because whenever there is a failure the normal level of safety is reduced?
I calculate that for the Hyd failure case the fully factored distance is approx 5590m, a significant increase compared to 3300m available - I am not suggest that 5590 is a ‘must have’ distance, it’s for comparison. So what are the justifications for accepting a low ‘safety factor’ of approx 1.06 (3300/3120) vs the standard factor of 1.97 (wet factored failure case 5590/3120).
In exceptional circumstances the Captain has the authority to accept additional risk, i.e. lower the level of safety. Is the hydraulic failure a qualifying event? This depends on many other aspects of the situation, particularly the availability of a suitable runway. Is this what Airbus state, imply, or leave open to the operators interpretation in calculating risk (and bearing the responsibility). In the failure case, the question to be considered is ‘should we be making this landing’, not ‘can we make this landing’.
However, confining the discussion to 3300m available and using the actual landing distance as the basis (Decision made - yes we should be making this landing, even after considering the distances involved, because there is no other alternative runway), then the calculations above should be used to quantify the change in risk – the level of safety of the planned operation. Thus equally important are the changes to procedures, operating conditions, specific actions, etc, based on the additional risk and any particular characteristics of the runway/airport in this situation, i.e. this is not just a landing distance question it is one of risk management.
I base my comments on the UK CAA AIC 14/2006 ‘Landing performance of large transport aeroplanes.’ I quote -
“2.3 This gross distance (actual) should be regarded as a theoretical minimum, consistent achievement of which requires a high level of pilot skill under favourable conditions, and concluding in a level of deceleration that would normally be considered excessive from the passenger comfort point of view. Consequently, in order to provide an operationally realistic level of performance, this gross distance is multiplied by a field length factor to obtain the Landing Distance Required.
2.4 This factor accounts for the normal operational variability that can be expected in day to day service such that the chances of a landing overrun are remote. It should be appreciated that the value of the factor is not the same for all aeroplane types. For example, propeller aeroplanes are not as sensitive to excessive approach speeds as are jet aeroplanes, consequently they are subject to a smaller factor.”
“6.2 Where a failure occurs in flight to other systems (eg restricted use of high lift devices) crews will normally be provided with advice on their effect on landing distance. Allowing for the low probability of such an occurrence, lower safety factors, if any, may have been applied compared to those used for the normal conditions. Therefore, even when such performance corrections are taken into account there may be a reduction in safety margins available to account for variations in, for example, touchdown accuracy or stopping technique. Other conditions, such as reduced wind limits, may also apply in such cases.”
So for a 3300m runway using a relative safety factor of 1.06 / 1.97 as a guide to the risk involved, and also against the need for “a high level of pilot skill under favourable conditions”; then do you land on 3300m?
If yes, what additional restrictions and guidance would be given? If operational managers cannot be assured that every pilot will be able to provide the high level of skill required on that day or in those particular circumstances (wee-one, you cannot determine “P1 non-factored landing distance’), then are they prepared to mitigate the consequences of landing (or overrun), because they, like the crew may have no other options when deciding to land.
Avoid wet runways?
So why should we accept a significant reduction in safety margin in the use of 3120m as opposed to the fully factored distance? Is this because whenever there is a failure the normal level of safety is reduced?
I calculate that for the Hyd failure case the fully factored distance is approx 5590m, a significant increase compared to 3300m available - I am not suggest that 5590 is a ‘must have’ distance, it’s for comparison. So what are the justifications for accepting a low ‘safety factor’ of approx 1.06 (3300/3120) vs the standard factor of 1.97 (wet factored failure case 5590/3120).
In exceptional circumstances the Captain has the authority to accept additional risk, i.e. lower the level of safety. Is the hydraulic failure a qualifying event? This depends on many other aspects of the situation, particularly the availability of a suitable runway. Is this what Airbus state, imply, or leave open to the operators interpretation in calculating risk (and bearing the responsibility). In the failure case, the question to be considered is ‘should we be making this landing’, not ‘can we make this landing’.
However, confining the discussion to 3300m available and using the actual landing distance as the basis (Decision made - yes we should be making this landing, even after considering the distances involved, because there is no other alternative runway), then the calculations above should be used to quantify the change in risk – the level of safety of the planned operation. Thus equally important are the changes to procedures, operating conditions, specific actions, etc, based on the additional risk and any particular characteristics of the runway/airport in this situation, i.e. this is not just a landing distance question it is one of risk management.
I base my comments on the UK CAA AIC 14/2006 ‘Landing performance of large transport aeroplanes.’ I quote -
“2.3 This gross distance (actual) should be regarded as a theoretical minimum, consistent achievement of which requires a high level of pilot skill under favourable conditions, and concluding in a level of deceleration that would normally be considered excessive from the passenger comfort point of view. Consequently, in order to provide an operationally realistic level of performance, this gross distance is multiplied by a field length factor to obtain the Landing Distance Required.
2.4 This factor accounts for the normal operational variability that can be expected in day to day service such that the chances of a landing overrun are remote. It should be appreciated that the value of the factor is not the same for all aeroplane types. For example, propeller aeroplanes are not as sensitive to excessive approach speeds as are jet aeroplanes, consequently they are subject to a smaller factor.”
“6.2 Where a failure occurs in flight to other systems (eg restricted use of high lift devices) crews will normally be provided with advice on their effect on landing distance. Allowing for the low probability of such an occurrence, lower safety factors, if any, may have been applied compared to those used for the normal conditions. Therefore, even when such performance corrections are taken into account there may be a reduction in safety margins available to account for variations in, for example, touchdown accuracy or stopping technique. Other conditions, such as reduced wind limits, may also apply in such cases.”
So for a 3300m runway using a relative safety factor of 1.06 / 1.97 as a guide to the risk involved, and also against the need for “a high level of pilot skill under favourable conditions”; then do you land on 3300m?
If yes, what additional restrictions and guidance would be given? If operational managers cannot be assured that every pilot will be able to provide the high level of skill required on that day or in those particular circumstances (wee-one, you cannot determine “P1 non-factored landing distance’), then are they prepared to mitigate the consequences of landing (or overrun), because they, like the crew may have no other options when deciding to land.
Avoid wet runways?
Mutt, where does the minimum ‘conversion’ of 1.15 come from? You appear to have used it as a means of determining the actual wet landing distance, although you note that the book value is larger - possibly because they are not related by a simple conversion.
My understanding (as above) is that for operational certification, a ‘field length factor’ is applied to actual distance to provide an additional level of safety - the required landing distance. An additional distance equal to 15% (1.15) of the factored dry distance should be added when operating on wet runways. This is a minimum distance for operational certification, but operators may increase this according to circumstance. Have I misunderstood something here?
Applying multipliers to aircraft landing distances is not the same as adding field length safety factors; the latter are an attempt to maintain a level of safety and not necessarily about where the aircraft will stop, although in practice they may be a good guide.
Were you relating 1.15 to the recent FAA guidance material? I found it confusing; I would appreciate a pilot’s guide to what it means or might mean in relationship to the discussion in this thread.
My understanding (as above) is that for operational certification, a ‘field length factor’ is applied to actual distance to provide an additional level of safety - the required landing distance. An additional distance equal to 15% (1.15) of the factored dry distance should be added when operating on wet runways. This is a minimum distance for operational certification, but operators may increase this according to circumstance. Have I misunderstood something here?
Applying multipliers to aircraft landing distances is not the same as adding field length safety factors; the latter are an attempt to maintain a level of safety and not necessarily about where the aircraft will stop, although in practice they may be a good guide.
Were you relating 1.15 to the recent FAA guidance material? I found it confusing; I would appreciate a pilot’s guide to what it means or might mean in relationship to the discussion in this thread.
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Alf I typed PI (eye) not P1. Performance in flight in boeing qrh.
The distances derived are unfactored. Or they have wasted ink typing that specific phrase. Jar 1.51 does not REQUIRE any further factoring, when using these charts to determine landing distance DURING a flight.. These are actual distances achievable. The non normal charts have different distances for different problems. The emergy effect is allowed for but they are still unfactored vis a vis LDR.
I have tried to make two points.
1 There is no requirement to factor under jar after the flight is dipatched.Factoring is a function of perf A probablity, not actual on the day.
2 Factoring of PI data is an operational option not a requirement.
To assume that operators that choose to use actual data in these circumstances are dangerous is unfair. The data doesnt support that and the achievable results on line and in the sim demonstrate that factoring is an academic safety proceedure to achieve the probabilty that perf a is based on.
If you factored the ldr for an urgent heavy 763 problem with no fuel dump you would be looking a long time for a runway long enough to land.
An average long runway in this case being 3000m would require a PI Base distance of approx 1550 meteres. So lets say the PI unfactored distance (from the PI non normal charts) was 1900 metres and its wet. LDR then becomes 1900x1.67x1.15=3648m ldr.
It starts to get silly distances very quickly. Mlud the defence rests
The distances derived are unfactored. Or they have wasted ink typing that specific phrase. Jar 1.51 does not REQUIRE any further factoring, when using these charts to determine landing distance DURING a flight.. These are actual distances achievable. The non normal charts have different distances for different problems. The emergy effect is allowed for but they are still unfactored vis a vis LDR.
I have tried to make two points.
1 There is no requirement to factor under jar after the flight is dipatched.Factoring is a function of perf A probablity, not actual on the day.
2 Factoring of PI data is an operational option not a requirement.
To assume that operators that choose to use actual data in these circumstances are dangerous is unfair. The data doesnt support that and the achievable results on line and in the sim demonstrate that factoring is an academic safety proceedure to achieve the probabilty that perf a is based on.
If you factored the ldr for an urgent heavy 763 problem with no fuel dump you would be looking a long time for a runway long enough to land.
An average long runway in this case being 3000m would require a PI Base distance of approx 1550 meteres. So lets say the PI unfactored distance (from the PI non normal charts) was 1900 metres and its wet. LDR then becomes 1900x1.67x1.15=3648m ldr.
It starts to get silly distances very quickly. Mlud the defence rests
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this is not just a landing distance question it is one of risk management.
Everything(!) in aviation is risk management! Stepping into an aircraft deciding to fly is risk management.
I'll always be happy to land on runways that fulfill the JAR required distance (my operator requires it that way in all cases except emergency).
When I have a heavy technical problem, or I need to divert immediatly (smoke), I will choose the next airports in my immediate range, choose the best runway for my needs (length, width, state, crosswind, type of approach etc...) and will land there.
And in some cases I'll have to land with actual landing distances with only little safety margin (for example + 8% for 5kt high on Vapp).
Everything(!) in aviation is risk management! Stepping into an aircraft deciding to fly is risk management.
I'll always be happy to land on runways that fulfill the JAR required distance (my operator requires it that way in all cases except emergency).
When I have a heavy technical problem, or I need to divert immediatly (smoke), I will choose the next airports in my immediate range, choose the best runway for my needs (length, width, state, crosswind, type of approach etc...) and will land there.
And in some cases I'll have to land with actual landing distances with only little safety margin (for example + 8% for 5kt high on Vapp).
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"factoring after dispatch phase"
JAR–OPS 1.475 General
(a) An operator shall ensure that the mass of
the aeroplane:
(1) At the start of the take-off;
or, in the event of in-flight replanning
(2) At the point from which the revised
operational flight plan applies,
is not greater than the mass at which the
requirements of the appropriate Subpart can be
complied with for the flight to be undertaken,...etc.
(a) An operator shall ensure that the mass of
the aeroplane:
(1) At the start of the take-off;
or, in the event of in-flight replanning
(2) At the point from which the revised
operational flight plan applies,
is not greater than the mass at which the
requirements of the appropriate Subpart can be
complied with for the flight to be undertaken,...etc.
Does this not mean that in the event of an in-flight replanning, same factors apply as during planning phase/dispatch?
If you have the answer, please let me know where it can be found as well.
If you have the answer, please let me know where it can be found as well.
z3
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I would say "yes", an inentional replanning BY CHOICE would be subject to the same restrictions as pre-flight planning. (Anything else would be ridiculous, as you could otherwise routinely "replan" 1 minute after takeoff and legally ignore every rule in the book!)
But that requirement wouldn't be interpreted to apply to abnormal or emergency conditions. Even if it DID, there's a "notwithstanding clause" in JAR-OPS which says, in effect, that you can break any rules you like in an emergency, anyway.
But that requirement wouldn't be interpreted to apply to abnormal or emergency conditions. Even if it DID, there's a "notwithstanding clause" in JAR-OPS which says, in effect, that you can break any rules you like in an emergency, anyway.
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I totally agree with you, Scientist. Re-planning by choice (company's choice?) is a completely different situation from the "emergency" case, and (based on JAR-OPS) it seems obvious that the same factors should apply - why reduce the safety margins during normal operations just because you're airborne?
Other thoughts or opinions, anyone?
Other thoughts or opinions, anyone?
“Does this not mean that in the event of an in-flight replanning, same factors apply as during planning phase/dispatch?”
Yes. JAR-OPS 1.515 requires a landing distance factor without reference to the aircraft being before or after the ‘start of the take-off’. So while 1.475 ensures that the aircraft is within all of the mass limitations for flight and the planned landing, 1.515 requires a landing factor for the planned landing and in-flight diversion. Abnormal or emergency operations would be considered on ‘merit’ as discussed in this thread. Note that IEM 515(c) requires the before takeoff plan to be based on a lower landing mass if ‘other considerations’ apply i.e. longest runway not available due to ATC, noise restrictions, wind, etc.
Re stopping with double Hyd failure: I assume that steering could be limited, thus asymmetric reverse might be used (if available) when the rudder effectiveness decreases (even if that is available with the failure). Using reverse for directional control may increase the ‘actual’ landing distance. Also, the amount of directional control could be limited in a crosswind (particularly on a wet runway), so there may be additional limits in those conditions i.e. landing distance could vary with crosswind.
Is there any manufacturer’s advice on these issues, or is this also the crew’s responsibility to manage the risks? The management process has to take into account all considerations (and consequences) of rare system failures; the manufacturer may only provide a stopping distance as it would impracticable to cover all foreseeable circumstances.
Yes. JAR-OPS 1.515 requires a landing distance factor without reference to the aircraft being before or after the ‘start of the take-off’. So while 1.475 ensures that the aircraft is within all of the mass limitations for flight and the planned landing, 1.515 requires a landing factor for the planned landing and in-flight diversion. Abnormal or emergency operations would be considered on ‘merit’ as discussed in this thread. Note that IEM 515(c) requires the before takeoff plan to be based on a lower landing mass if ‘other considerations’ apply i.e. longest runway not available due to ATC, noise restrictions, wind, etc.
Re stopping with double Hyd failure: I assume that steering could be limited, thus asymmetric reverse might be used (if available) when the rudder effectiveness decreases (even if that is available with the failure). Using reverse for directional control may increase the ‘actual’ landing distance. Also, the amount of directional control could be limited in a crosswind (particularly on a wet runway), so there may be additional limits in those conditions i.e. landing distance could vary with crosswind.
Is there any manufacturer’s advice on these issues, or is this also the crew’s responsibility to manage the risks? The management process has to take into account all considerations (and consequences) of rare system failures; the manufacturer may only provide a stopping distance as it would impracticable to cover all foreseeable circumstances.
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Where a failure case covered by a single flight manual procedure has handling difficulties or special procedures, these will be noted in the relevant procedure (such as advice to minimize brake pumping in the event of multiple hyd failures, if your brake system is running on accumulator power only).
A double or multiple failure which is not the subject of a specific AFM abnormal or emergency procedure may have handling or other problems due to the combined effects; these may not be identified, since there won't be a "engine fire plus depressurisation" procedure to follow, and the problem may ONLY exist in the combined case. In that case it is indeed on the shoulders of the crew's basic airmanship skills.
The idea is that such 'perfect storm' days are so rare that they should not be provided for, as there are such a huge number of combinations, each of which is very unlikely indeed.
PS obviously, those remarks apply specifically to our manuals, but I don't believe we're significantly different from other OEMs.
Edit: to clarify - usually double hyd failure is a sufficiently probable event that a specific procedure exists, which would include some or all of the advice suggested, dependent upon model.
A double or multiple failure which is not the subject of a specific AFM abnormal or emergency procedure may have handling or other problems due to the combined effects; these may not be identified, since there won't be a "engine fire plus depressurisation" procedure to follow, and the problem may ONLY exist in the combined case. In that case it is indeed on the shoulders of the crew's basic airmanship skills.
The idea is that such 'perfect storm' days are so rare that they should not be provided for, as there are such a huge number of combinations, each of which is very unlikely indeed.
PS obviously, those remarks apply specifically to our manuals, but I don't believe we're significantly different from other OEMs.
Edit: to clarify - usually double hyd failure is a sufficiently probable event that a specific procedure exists, which would include some or all of the advice suggested, dependent upon model.
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Boeing Dreamliner wet runway test in Roswell, N.M.
Video of Boeing 787 Dreamliner wet runway test in Roswell, N.M. at this link
Video of Boeing 787 Dreamliner wet-runway tests in N.M.
Video of Boeing 787 Dreamliner wet-runway tests in N.M.
