Landing Performance
Mach 3
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Landing Performance
Can anyone point me to the JAR reference that deals with the allowable speed spreads at the threshold + 50ft when calculating landing distances required?
I know its -5/+15kts but can't find it anywhere....
Thanks.
I know its -5/+15kts but can't find it anywhere....
Thanks.
Mach 3
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Martin,
I had a look at JAR 25.125.
Is my understanding correct, then, that if your permissible tailwind component is 10kts, the +15kts increment on Vref takes into account the 150% of the tailwind aspect of the calculation?
This is obviously the limiting case contrast a headwind situation...
I had a look at JAR 25.125.
Is my understanding correct, then, that if your permissible tailwind component is 10kts, the +15kts increment on Vref takes into account the 150% of the tailwind aspect of the calculation?
This is obviously the limiting case contrast a headwind situation...
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I don't have the JAR 25, but I do have the JAR-OPS, which says that an airplane should be able to stop within 60% of the LDA(Jets).
From JAR-OPS 1.515 - Landing Dry RWY:
An operator must take into account of the following:
a) the altitude of the aerodrome,
b) Not more than 50% of the head-wind component or not less than 150% of the tail-wind component,
c) the runway slope in the direction of landing if greater than +/-2%
Another thing the airplane shall be able to climb with one engine out in approach config with a gradient of 2.5%.
So operational you should put a half headwind component or 150% of the tail wind to you Vref. ex. Vref: 142kts headwind 12kts Vapp: 148kts
Martin
From JAR-OPS 1.515 - Landing Dry RWY:
An operator must take into account of the following:
a) the altitude of the aerodrome,
b) Not more than 50% of the head-wind component or not less than 150% of the tail-wind component,
c) the runway slope in the direction of landing if greater than +/-2%
Another thing the airplane shall be able to climb with one engine out in approach config with a gradient of 2.5%.
So operational you should put a half headwind component or 150% of the tail wind to you Vref. ex. Vref: 142kts headwind 12kts Vapp: 148kts
Martin
Moderator
It can get a bit confusing .. some things to consider (and I don't propose to hold myself out as having any particular knowledge of JARs as opposed to FARs)
(a) if the AFM data is factored, then the 50/150 is in the grid and the wind is entered as observed. Simple way to tell if the factor is in is to see if the wind grid (carpet) lines are discontinuous (ie have a kink) at nil wind .. if the grid is unfactored, then the curves will be smooth as you go through the nil wind case. In the latter case, you would need to apply the factor prior to using the chart.
(b) I can't ever recall seeing anything definitive re approach margins (not to say such doesn't exist) and I suggest that the thing is more a risk management approach to the problem .. considerations -
(i) excess speed additives .. main problem is over run on a critical length runway .. if you run some simple calcs for the 1.67 case, and typical Vref, the Vref+20 max idea seems to make reasonably good sense.
(ii) one should always strive NOT to be under Vref at all .. the margins aren't all that great to start with and, on some aircraft, a few knots under can make a big difference to the pilot pucker factor .. 727-200 comes to mind
(c) other things which may need to be looked at .. pitching moment problems (probably only a concern for takeoff in excessive tailwind on susceptible Types), missed approach pilot control loads, (if the AFM only gives you 10 kt tail and you propose to increase that) some requirements in Part 25 are based on 10 kt and may require a revisit if one intends to extend beyond 10 kt.
Two concerns ..
(a) .. but I do have the JAR-OPS, which says that an airplane should be able to stop within 60% of the LDA(Jets)...
If you believe that (uncritically) then I have a bridge to sell you. The normal heavy certification basis is that the demonstrated LD is factored by 1.67 to arrive at the LDR. Keep in mind that
(i) the flight test program is geared to get the "best" data within the bounds of test pilot and program integrity .. let me put it this way .. the most terrifying experiences I have ever had in an aeroplane have been performance landing tests with a TP motivated by a desire to get "good" data .. There will be far more trials done than required .. the TP is quite at liberty to nominate a few to be discarded (no prizes for guessing which ones get their marching orders). Then the aerodynamicists throw out a few more (likewise).
(ii) I know that the design rules say something along the lines of "normal pilot capabilities" ... mmmm
(iii) take it as near gospel .. if you are on a limiting runway and approach through the AFM gate, on speed, you have a near guaranteed likelihood of seeing the dirt at the other end .. intimately.
That is to say, be very careful using, eg, unfactored QRH data without thinking carefully what you are doing ..
(b) ...So operational you should put a half headwind component or 150% of the tail wind to you Vref. ex. Vref: 142kts headwind 12kts Vapp: 148kts...
This is worth discussing further ... somewhere between misguided and dangerous, I would suggest ? More to the point, in my view, it is irrelevant to the approach additive question and only applies to the distance calculations ... ?
I'm being very serious in hoping that this thread develops as there is a number of aspects of approach and landing number crunching which are not all that well understood by the fraternity ...
(a) if the AFM data is factored, then the 50/150 is in the grid and the wind is entered as observed. Simple way to tell if the factor is in is to see if the wind grid (carpet) lines are discontinuous (ie have a kink) at nil wind .. if the grid is unfactored, then the curves will be smooth as you go through the nil wind case. In the latter case, you would need to apply the factor prior to using the chart.
(b) I can't ever recall seeing anything definitive re approach margins (not to say such doesn't exist) and I suggest that the thing is more a risk management approach to the problem .. considerations -
(i) excess speed additives .. main problem is over run on a critical length runway .. if you run some simple calcs for the 1.67 case, and typical Vref, the Vref+20 max idea seems to make reasonably good sense.
(ii) one should always strive NOT to be under Vref at all .. the margins aren't all that great to start with and, on some aircraft, a few knots under can make a big difference to the pilot pucker factor .. 727-200 comes to mind
(c) other things which may need to be looked at .. pitching moment problems (probably only a concern for takeoff in excessive tailwind on susceptible Types), missed approach pilot control loads, (if the AFM only gives you 10 kt tail and you propose to increase that) some requirements in Part 25 are based on 10 kt and may require a revisit if one intends to extend beyond 10 kt.
Two concerns ..
(a) .. but I do have the JAR-OPS, which says that an airplane should be able to stop within 60% of the LDA(Jets)...
If you believe that (uncritically) then I have a bridge to sell you. The normal heavy certification basis is that the demonstrated LD is factored by 1.67 to arrive at the LDR. Keep in mind that
(i) the flight test program is geared to get the "best" data within the bounds of test pilot and program integrity .. let me put it this way .. the most terrifying experiences I have ever had in an aeroplane have been performance landing tests with a TP motivated by a desire to get "good" data .. There will be far more trials done than required .. the TP is quite at liberty to nominate a few to be discarded (no prizes for guessing which ones get their marching orders). Then the aerodynamicists throw out a few more (likewise).
(ii) I know that the design rules say something along the lines of "normal pilot capabilities" ... mmmm
(iii) take it as near gospel .. if you are on a limiting runway and approach through the AFM gate, on speed, you have a near guaranteed likelihood of seeing the dirt at the other end .. intimately.
That is to say, be very careful using, eg, unfactored QRH data without thinking carefully what you are doing ..
(b) ...So operational you should put a half headwind component or 150% of the tail wind to you Vref. ex. Vref: 142kts headwind 12kts Vapp: 148kts...
This is worth discussing further ... somewhere between misguided and dangerous, I would suggest ? More to the point, in my view, it is irrelevant to the approach additive question and only applies to the distance calculations ... ?
I'm being very serious in hoping that this thread develops as there is a number of aspects of approach and landing number crunching which are not all that well understood by the fraternity ...
UK CAA AIC 11/98 “Landing performance of large transport aeroplanes” provides an excellent briefing on the margins assumed for airspeed etc at the threshold, noting that the margins are for safety reasons to accommodate error and not for use in planned operations. Also note that any margin may not protect against error in more than one variable i.e. fast and a long landing.
The aircraft manufacturer may recommend additions to the calculated threshold speed for wind, wind-gust, or stall margin in icing conditions. The ‘performance’ threshold speed is a single value – no spread. The assumptions and procedures associated with use of the increased ‘operational’ speeds have to be heeded, e.g. an aircraft making a ‘standard’ Vref + 10 approach is expected to reduce speed before the threshold (or during the flare) to achieve the ‘performance’ speed at touchdown (approx Vref -7). In some aircraft an icing additive may incur a landing distance penalty if the approach speed is increased above Vref +7 i.e. +2% landing dist for every kt above Vref + 7, refer to your aircraft manual.
Also see JAA NPA 14 Operation on Contaminated Runways – (JAR 25 1591 / AMC 25.1591). I will provide a link to this and the AIC when back at base.
In addition, there is a good overview and many references for landing operations, including speeds in the presentation and speaker notes of ALAR TEM.
The aircraft manufacturer may recommend additions to the calculated threshold speed for wind, wind-gust, or stall margin in icing conditions. The ‘performance’ threshold speed is a single value – no spread. The assumptions and procedures associated with use of the increased ‘operational’ speeds have to be heeded, e.g. an aircraft making a ‘standard’ Vref + 10 approach is expected to reduce speed before the threshold (or during the flare) to achieve the ‘performance’ speed at touchdown (approx Vref -7). In some aircraft an icing additive may incur a landing distance penalty if the approach speed is increased above Vref +7 i.e. +2% landing dist for every kt above Vref + 7, refer to your aircraft manual.
Also see JAA NPA 14 Operation on Contaminated Runways – (JAR 25 1591 / AMC 25.1591). I will provide a link to this and the AIC when back at base.
In addition, there is a good overview and many references for landing operations, including speeds in the presentation and speaker notes of ALAR TEM.
Here are the links to references in UK Aeronautical Information Service (AIS). Subscription is required (free), well worth the effort just to view the valuable safety information. Select, Subscribe here; or (when registered), Publications, UK AIC, Pink(P), for the safety material.
The reference I quoted above (UK CAA AIC 11/98) has been revised; see:-
‘Landing performance of large transport aeroplanes’ 14(P91)/2006, also see
‘Risks and factors associated with operations on runways affected by snow, slush or water’ 15(P92)/2006
The widely quoted speed margin at the threshold of Vref+15 probably originates from the old ‘reference’ method of determining the certified landing performance. Although these tests would have been conducted on a wet runway the resulting performance could vary due to the variability in runway mu, surface, etc.
JT your experiences with a test team may have been exciting, but they reflect the ‘arbitrary’ method of determining the gross (unfactored) landing distance, which as the AIC states is only a theoretical value. For the discarded tests, it is more likely that the test pilot assessed that not all of the parameters were met, thus reflecting the difficult (impossible) task of achieving the unfactored distance in daily operations. I reiterate your warning be very careful using, unfactored QRH data without thinking carefully what you are doing ..
The most valuable thought is ‘should I be making this approach and landing in these conditions’, not can I make the approach and landing.
The factored landing distance of 1.67 accommodates the FAR “land within 60% of LDA”; JAR OPS requires a further 15% factor for wet runways resulting in a 1.92 safety factor. The resulting distances only provide a safety margin. Safety is never absolute, only relative, i.e. studies in Canada suggest that a factor of 2.2 - 2.4 times the unfactored landing distance is required for some contaminated operations in order to achieve the equivalent margin of safety for landing on a dry runway. There are many pitfalls in the area of relative safety i.e. beware of JAR-OPS allowing wet ‘grooved’ runways being defined as ‘dry’, all this does is reduce the safety margin within ‘acceptable’ limits – acceptable to the authority, but (as usual) the final responsibility rests with the operator / captain.
The use (or abuse) of speed additives is a major factor in determining a safe landing. The AIC concludes “The highest degree of confidence in successfully achieving the scheduled landing distances is obtained by crossing the threshold at the correct height and at the target threshold speed, touching down firmly after a normal flare and applying maximum retardation without delay.”
Headwind / tailwind corrections are in the tables of factored landing distance (or computed data).
Approach speed additives for wind gusts or turbulence, icing, etc, are operator defined adjustments which have to balance the margin of safety achieved when using Vref, with any reduction of safety margin at a higher speed. The final balance is the overall safety of the operation, thus a speed addition can be safer from a gust/windshear perspective, but less safe from a landing/stopping aspect – check recent accidents. How many stalls on the approach vs the number of overruns!
An aircraft certification requires a demonstration of a safe landing from Vref -5 (in good conditions). Thus a normal approach at Vref +5 already has a 10 kt gust margin, any further addition should be seen as a speed target (something to aim for) and not a minimum. Normally speed adjustments are not accumulative except for specific increases in icing conditions. In these cases the AFM may mandate a longer LDR. The certification may also limit the maximum threshold speed, taking into consideration the chance of a nose-wheel first landing or delayed wt-on-wheels switching that could prevent immediate reverser or brake operation.
The reference I quoted above (UK CAA AIC 11/98) has been revised; see:-
‘Landing performance of large transport aeroplanes’ 14(P91)/2006, also see
‘Risks and factors associated with operations on runways affected by snow, slush or water’ 15(P92)/2006
The widely quoted speed margin at the threshold of Vref+15 probably originates from the old ‘reference’ method of determining the certified landing performance. Although these tests would have been conducted on a wet runway the resulting performance could vary due to the variability in runway mu, surface, etc.
JT your experiences with a test team may have been exciting, but they reflect the ‘arbitrary’ method of determining the gross (unfactored) landing distance, which as the AIC states is only a theoretical value. For the discarded tests, it is more likely that the test pilot assessed that not all of the parameters were met, thus reflecting the difficult (impossible) task of achieving the unfactored distance in daily operations. I reiterate your warning be very careful using, unfactored QRH data without thinking carefully what you are doing ..
The most valuable thought is ‘should I be making this approach and landing in these conditions’, not can I make the approach and landing.
The factored landing distance of 1.67 accommodates the FAR “land within 60% of LDA”; JAR OPS requires a further 15% factor for wet runways resulting in a 1.92 safety factor. The resulting distances only provide a safety margin. Safety is never absolute, only relative, i.e. studies in Canada suggest that a factor of 2.2 - 2.4 times the unfactored landing distance is required for some contaminated operations in order to achieve the equivalent margin of safety for landing on a dry runway. There are many pitfalls in the area of relative safety i.e. beware of JAR-OPS allowing wet ‘grooved’ runways being defined as ‘dry’, all this does is reduce the safety margin within ‘acceptable’ limits – acceptable to the authority, but (as usual) the final responsibility rests with the operator / captain.
The use (or abuse) of speed additives is a major factor in determining a safe landing. The AIC concludes “The highest degree of confidence in successfully achieving the scheduled landing distances is obtained by crossing the threshold at the correct height and at the target threshold speed, touching down firmly after a normal flare and applying maximum retardation without delay.”
Headwind / tailwind corrections are in the tables of factored landing distance (or computed data).
Approach speed additives for wind gusts or turbulence, icing, etc, are operator defined adjustments which have to balance the margin of safety achieved when using Vref, with any reduction of safety margin at a higher speed. The final balance is the overall safety of the operation, thus a speed addition can be safer from a gust/windshear perspective, but less safe from a landing/stopping aspect – check recent accidents. How many stalls on the approach vs the number of overruns!
An aircraft certification requires a demonstration of a safe landing from Vref -5 (in good conditions). Thus a normal approach at Vref +5 already has a 10 kt gust margin, any further addition should be seen as a speed target (something to aim for) and not a minimum. Normally speed adjustments are not accumulative except for specific increases in icing conditions. In these cases the AFM may mandate a longer LDR. The certification may also limit the maximum threshold speed, taking into consideration the chance of a nose-wheel first landing or delayed wt-on-wheels switching that could prevent immediate reverser or brake operation.
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alf - not sure whether
came from 11/98 but it is not in the current. Do you have a reference for this? I've spent years trying to stop F/Os panicking if they see less than Vref+5 + until they touch.
The FCTM (Boeing 737) suggests Vref+0 in a sort of veiled way.
‘performance’ speed at touchdown (approx Vref -7).
The FCTM (Boeing 737) suggests Vref+0 in a sort of veiled way.
BOAC
References:- FAA AC 121-95 ‘Operational Landing Distances for Wet Runways’ quotes a factor of 0.96 between threshold speed and touchdown. (However, this is probably a ‘required’ min speed loss during test flights to determine the min landing distance, i.e. prevents ‘no flare landings’ being used).
NPA 14-2004 Operation on Contaminated Runways provides the following information which I believe originates from the certification assumptions/calculations in wet/dry operations.
There is additional explanation in the comment pages.
Thus for a Vref of 100kts the speed loss is 7 kts, but this may be greater if test data shows otherwise.
IIRC several manufactures have used/assumed (at least in casual discussion) a 7 kt loss in determination of landing performance. Some auto land systems either have 7tks as a target speed loss, or it is the resultant of the flare design. Most autoland flares are representative of manual landings.
Again CAA data analyzing steep approach landings on one aircraft type indicated a 7kt loss in the flare; perhaps normal approach angles would result in a greater speed loss.
Overall a 7 kt loss appears to be an approximation to the certification requirements above, covering a range of large aircraft types and operating weights.
References:- FAA AC 121-95 ‘Operational Landing Distances for Wet Runways’ quotes a factor of 0.96 between threshold speed and touchdown. (However, this is probably a ‘required’ min speed loss during test flights to determine the min landing distance, i.e. prevents ‘no flare landings’ being used).
NPA 14-2004 Operation on Contaminated Runways provides the following information which I believe originates from the certification assumptions/calculations in wet/dry operations.
7.4.2 Landing Air Distance - For contaminated surfaces, the airborne distance should be calculated by assuming that 7 seconds elapse between passing through the 50 ft screen height and touching down on the runway. In the absence of flight test data to substantiate a lower value, the touchdown speed should be assumed to be 93% of the threshold speed.
Thus for a Vref of 100kts the speed loss is 7 kts, but this may be greater if test data shows otherwise.
IIRC several manufactures have used/assumed (at least in casual discussion) a 7 kt loss in determination of landing performance. Some auto land systems either have 7tks as a target speed loss, or it is the resultant of the flare design. Most autoland flares are representative of manual landings.
Again CAA data analyzing steep approach landings on one aircraft type indicated a 7kt loss in the flare; perhaps normal approach angles would result in a greater speed loss.
Overall a 7 kt loss appears to be an approximation to the certification requirements above, covering a range of large aircraft types and operating weights.
Could someone explain how to register on 'UK Aeronautical Information Service (AIS)' without having a UK address? The registration will not accept a post code which does not have letters in it.
