B737 Landing Distance Question

[KazohiroNakamura]

According to the regulations, you have to be able to stop your A/C within 60% of the LDA. So a factor of 1.67 on the Landing Distance required. And if the runway is wet is should be +15% so in total is would be 1.92 of the Landing Distance required.

Is this a performance dispatch requirement or do you need to use these figures also once you are in the air?

If not, what factor do you add to your landing distance in reality?

Let's assume you don't have the landing performance on board and you have to use the QRH only.

And what about when the runway is contaminated for landing. Do you use the Performance Inflight Normal Configuration Landing Distances for the reported braking action? With or without a factor?

Thanks in advance!

Nakamura

[safetypee]

See this thread http://www.pprune.org/tech-log/471353-required-landing-distance-available-does-inflight-requirement-exist.html

For a contaminated runway see the link in post #4.

Discuss.

[KazohiroNakamura]

Pfff.... After reading it all I have more questions than answers http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/wink2.gif

4.2 Before commencing an approach, the commander is required to ensure that a safe approach and landing can be made given the updated meteorological and runway surface condition (see EU-OPS 1.400). The operator is required to demonstrate that it can ensure safe operations, and by applying the same additional safety margin to the in-flight performance assessment as to the dispatch assessment demonstrates an equivalent level of safety. SAFO 06012 also recommends an additional safety margin of at least 15% on actual landing distance, except in an emergency.

4.3 The safety margins required by EU-OPS reflect the rare occasions an operator would find themselves operating on contaminated runways. Operators wishing to operate on contaminated runways on a more regular basis would be required to demonstrate to the National Aviation Authority an equivalent level of safety comparable to operations on non-contaminated runways. An acceptable means has been for the operator to apply company safety margins and additional required distances to the performance derived. Approved AFM contaminated performance data that has been derived from analysis and theoretical calculation of the demonstrated and certified dry runway ALD has sometimes been found not to reflect the aircraft performance achieved. Research (as yet unpublished) is suggesting that a factor of up to 1.32 would more accurately reflect the performance the aircraft is likely to achieve, and a factor of up to 1.41 where reference information for operational corrections for runway slope and temperature is not available. These factors would obviously have an impact on the operator’s dispatch and in-flight assessment requirements. The very recent development of OLD provides more realistic data of the aircraft landing performance but due to calculation assumptions, which include piloting accuracy, it is also appropriate and likely to be mandated that it includes a safety margin factor of 1.15. This also appears to be in line with FAA proposals. Operator analysis of the data from their FDM programmes, specifically looking at the piloting assumptions in the calculation of OLD, may lead the operator to increasing the factor further.

So first @ 4.2 they tell us to use the same safety margins inflight as we do for planning.

Then @ 4.3 they explain that a margin of 1.41 is acceptable.

I am confused nowhttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/confused.gifhttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/confused.gif

Also they don't mention the 60% (1.67)

[Pub User]

I think you may be getting the distances mixed up.

Dispatch requirement is 1.67 dry, and 1.92 wet, of the DRY landing distance.

Dispatch to a contaminated runway requires 1.15 times the CONTAMINATED landing distance, or the wet figure if it is greater.

Once airborne, their suggested factor for a contaminated runway is 1.32 times the CONTAMINATED distance, this is not (yet?) a legal requirement.

[KazohiroNakamura]

@Pub User

Dispatch to a contaminated runway requires 1.15 times the CONTAMINATED landing distance, or the wet figure if it is greater.

But if you look up the figures in the QRH for contaminated runway. They are already factored by the 15%

As far as landing requirements INFLIGHT

On the 737 Performance Reference Handbook, it states that the only 2 requirements are:

1. LDR < LDA
2. Required go-around climb gradient must be achieved.

And they recommend to increase the LDR by 15% if the runway is not dry.

[Pub User]

Those are Boeing's performance recommendations, not the Authority's legal requirements.

[KazohiroNakamura]

Ok, so what are you suggesting to do for a normal landing (dry) having only your QRH. Do you just take the distance stated in the QRH (LDR) and check if it is less than the LDA? Without any factor applied on your LDR?

[JammedStab]

According to the regulations, you have to be able to stop your A/C within 60% of the LDA. So a factor of 1.67 on the Landing Distance required. And if the runway is wet is should be +15% so in total is would be 1.92 of the Landing Distance required.

Is this a performance dispatch requirement or do you need to use these figures also once you are in the air?


Keep in mind that it can vary by country. In Canada, there are dispatch requirements but once in the air, you are allowed to go somewhere without the increased runway length of factoring, just the landing distance required as set out by the manufacturer. And remember that while they did not use any reverse on a bare, dry runway to come up with that distance, the test pilots were allowed to descend on a 3.5° glidepath and land very firmly. And, they don't calculate the added speed that you may have for gusts.

For dispatch, you have to do the multiplication times 1.67 plus 15% as you stated earlier if the runway may be wet according to forecast but if you have an alternate that is sufficient length to meet these requirements, you don't have to add the 15%. In other words, the longer alternate runway allows you to dispatch for the wet runway with dry runway distance factor only(1.67 instead of 1.92). Or a shorter length can be used if the manufacturer published wet landing performance that is shorter than the 1.92 times landing distance required but it can't ever be below the dry landing distance(such a situation might happen if reverse thrust, used for wet calculations but not dry, were very effective).

Remember, as wet landing distances are based on using reverse thrust, if you get into a situation where you have to cancel reverse as per procedure for regaining directional control, that is not accounted for.

Contaminated runway ops corrections(based on reverse thrust use) are advisory only.

[KazohiroNakamura]

Let me get my ducks in a row :)

So for planning purposes you need the 1,67 and if the runway is wet 1,92. And that is based on the most probable landing runway.

If by chance the runway changes upon arrival to a shorter on. You don't take into account the 1,67 and 1,92. You only add a 15% on top of the QRH figures is the runway is wet.

Can someone confirm if this is correct according to EU-OPS?

[de facto]

Qrh jaa factored (includes 15%)
QRH FAA NOT factored.
If the runway is changed or / and conditions change,adding 15% to unfactored distances is advised by the FAA(pilot skills/flare technique etc..).
Use qrh brake action good for runway WET.both JAA and FAA.

Clear?

[KazohiroNakamura]

It's clear!

Thx guys for the help a appreciate it. :ok:

[safetypee]

KN, clarity is not necessarily safety.
In EU-OPS, the commander is required to ensure a safe approach and landing (EU-OPS 1.400). Thus for wet/dry ops, the open question is if the chosen 15% of something (QRH) will be as safe as the pre-takeoff factor (1.67/1.92). There is no particular factor or distance margin specified for an inflight check. The pre-landing decision requires (re)assessment of all relevant conditions and the choice of safe action.
This assessment requires knowledge of what the QRH figures mean, what assumptions have been made and any limits in use. The Boeing unfactored ‘actual’ distances might only equate to a practical minimum distance flown in average conditions by an average pilot.
The pre-takeoff factored distances may enable greater variability in operation, and define a standard which the authority accepts as acceptably safe (acceptable risks – severity of event / frequency of encounter). Guidance on this is in UK AIC 14/06 http://www.ead.eurocontrol.int/pamslight/pdf/4e415453/EG/C/EN/AIC/EG_Circ_2006_P_014_en
Thus, does the QRH +15% (wet/dry conditions) provide an equivalent level of safety as would the pre-takeoff factored distance?

Contaminated operations are different. In the EU the authority accepts a lower level of safety assuming infrequent landings. However, the commander is still required to ensure safety.
The UK CAA have provided guidance which indicates that the (reduced) dispatch factor could be an acceptable safety margin, but cautions that because the distances may include the use of reverse, a reverse failure should be considered. Also, that some unpublished data suggests that contam+15% may not be achievable as a realistic minimum. The general advice in the EU for contaminated operations is to avoid the conditions (see CS-25.1591).

Comment on previous posts:
Wet AFM (unfactored) performance is more likely not to include the use of reverse (#8) - CS 25.125.
The use of ‘Good’ braking action in wet conditions is not the same as ‘good’ in dry conditions; ‘good’ is a relative term according to the actual conditions and not comparable across conditions (#10) - Managing Threats and Errors during Approach and Landing (http://www.skybrary.aero/bookshelf/content/bookDetails.php?bookId=874) slide 26.

[JammedStab]

Wet AFM (unfactored) performance is more likely not to include the use of reverse (#8) - CS 25.125.


For my clarification, are you saying that for wet AFM (unfactored) performance, reverse thrust credit is allowed but frequently not used by the manufacturer?

[safetypee]

The certification requirements only consider a dry runway (CS-25.125, FAR 25 similar). Wet runway performance is a multiple of dry performance, although many manufacturers will gather ‘wet’ data as a check.
The requirements do not prohibit the use of reverse or any other ‘device’:-
“Means other than wheel brakes may be used if that means –
(i) Is safe and reliable;
(ii) Is used so that consistent results can be expected in service; and
(iii) Is such that exceptional skill is not required to control the aeroplane.”

Few manufacturers elect to certificate their aircraft to this para, probably due to the complexities of proof of reliability, consistency of operation, and requiring separate data for engine failure:-

“If any device is used that depends on the operation of any engine, and if the landing distance would be noticeably increased when a landing is made with that engine inoperative, the landing distance must be determined with that engine inoperative unless the use of compensating means will result in a landing distance not more than that with each engine operating.”

Thus credit for reverse thrust during landing is generally not included in certificated landing performance.
EASA (CS-25 or alternative approved data) may allow reverse thrust for landing on contaminated runways, but as discussed previously the operator/commander has to consider the possibility of engine/reverse failure – a hint that a larger distance factor should be used.

For info, because wet performance is only a multiple of dry data, based on an intermediate wet friction value, the safety margin in some wet conditions may not be as good as for dry conditions. In some circumstances wet landings may have very small safety margin due to the variability of wet conditions (not flooded/contaminated runway), poor runway surface, tyre condition, etc.

[JammedStab]

The certification requirements only consider a dry runway (CS-25.125, FAR 25 similar). Wet runway performance is a multiple of dry performance, although many manufacturers will gather ‘wet’ data as a check.
The requirements do not prohibit the use of reverse or any other ‘device’:-
“Means other than wheel brakes may be used if that means –
(i) Is safe and reliable;
(ii) Is used so that consistent results can be expected in service; and
(iii) Is such that exceptional skill is not required to control the aeroplane.”

Few manufacturers elect to certificate their aircraft to this para, probably due to the complexities of proof of reliability, consistency of operation, and requiring separate data for engine failure:-

“If any device is used that depends on the operation of any engine, and if the landing distance would be noticeably increased when a landing is made with that engine inoperative, the landing distance must be determined with that engine inoperative unless the use of compensating means will result in a landing distance not more than that with each engine operating.”

Thus credit for reverse thrust during landing is generally not included in certificated landing performance.
EASA (CS-25 or alternative approved data) may allow reverse thrust for landing on contaminated runways, but as discussed previously the operator/commander has to consider the possibility of engine/reverse failure – a hint that a larger distance factor should be used.

For info, because wet performance is only a multiple of dry data, based on an intermediate wet friction value, the safety margin in some wet conditions may not be as good as for dry conditions. In some circumstances wet landings may have very small safety margin due to the variability of wet conditions (not flooded/contaminated runway), poor runway surface, tyre condition, etc.

To mostly quote from sources....

Wet runway performance does not have to be a multiple of dry distance(although it normally is). As an alternative method, manufacturers may conduct wet runway testing to determine the factored wet runway landing distances. The procedure, which is described in AC 121.195(d)-1A, differs somewhat from the dry runway testing requirements and has some built-in safety factors to account for possible deviations from the optimum flight profile. For wet runway testing, the landing distance is based on a 50–foot threshold crossing height to touchdown time of 7 seconds at an approach speed of 1.4 VS, and a touchdown speed that is 96% of the approach speed. Based on these parameters, the aircraft should be anticipated to touchdown approximately 1700 feet from the threshold, assuming a zero wind condition. Since this modified flight profile was intended to be more representative of the variables encountered during an actual landing which increase landing distance, AC 121.195(d)-1A calls for this distance to be increased by an additional factor of 1.15 “to assure operational safety”.


http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/b2a4ea852babd7b7862569f1006dc943/$FILE/AC121.195(d)-1A.pdf

Concerning Boeing, with the most jets out there, you are correct in that reverse thrust credit is not in the certification data.

However, some manufacturers or third party companies will produce a second set of landing performance charts, based on certification testing, which are supposed to give a more accurate determination of actual landing distance for operational use. This information is called advisory data, since it is based on recommended standard operating procedures which differ from certification testing.

Unlike the factored landing distance data, which is included in an AFM, advisory data typically includes a reverse thrust credit. Most advisory data begins with the unfactored dry runway landing distance. From there, analytical computations, rather than actual flight testing is typically used to determine the aircraft's landing performance on wet, snow-covered, or ice-covered runways.

For many of its newer aircraft, Boeing manuals include advisory data, in addition to the certified data. These charts, which are based on unfactored dry landing distances, include a number of landing distance adjustments based on braking configuration, weight, wind, runway slope, temperature, touchdown speed, reversers, and reported braking action.

Boeing began producing advisory data in the early 1990s when it changed to the current FCOM format.

In Europe, JAR–OPS 1 requires a factor of 1.15 be included in all wet/slippery runway advisory data as a safety margin.

Boeing will provide this advisory information upon request and it has been provided to non–JAR operators that requested the advisory data.

[safetypee]

JS, thanks for the info, I had overlooked AC 121.195. This is an extremely old AC, which IIRC was designed primarily for operators to obtain accurate wet (certificated) landing data. I am not aware of any manufacturer or operator using certificated data based on this standard.

As for Boeing or third party ‘actual’ data - published in the QRH (non-certificated), it is necessary to read the small print very carefully.
This data would not appear to meet the requirements of EU OPS-1 for pre-dispatch assessment. Furthermore if it were to be used in the EU OPS-1 pre landing check “to ensure a safe approach and landing”, it might be difficult to define a suitable additional safety distance factor which would equate to a level of safety implied in the pre dispatch calculations. Hence my post #12.

In the event of an incident in normal operation, reliance on reverse as in the QRH data, could be difficult to justify given the lack of reverse credit in certificated data.
Obviously in non-normal / emergency conditions the QRH data is invaluable, but this still requires knowledge of what assumptions are in the performance calculations, e.g speed and threshold accuracy and assumed touchdown position (which may not be achievable).
Whilst the recommendation to add 15% to wet/slippery performance (ill-defined terms) will aid safety, this margin may only result in a realistic minimum achievable landing distance, thus an additional safety margin should always be considered. Many operators / pilots see this recommendation as a necessary and legally sufficient minimum, which unfortunately several overrun accidents have shown not to be the case.

There are many gaps in the regulations and guidance material on this subject. It is difficult to quantify a specific distance margin or factor for every situation, thus the reliance on human judgement of ‘safe’ in the conditions perceived. Unfortunately the human suffers weaknesses in perception and judgement, but is also subject to incomplete data about runway condition and the assumptions in advisory landing data.

[JammedStab]

The Advisory data provided by Boeing and found in the Performance Inflight (PI) – section of the Quick Reference Handbook (QRH) is based on landings carried out in normal configuration. This Advisory data, which may also be referred to as “enroute data” or “operational” data, provided by Boeing has always been based on the use of reverse thrust.

http://www.ifalpa.org/downloads/Level1/Briefing%20Leaflets/Aircraft%20Design%20&%20Operation/12ADPBL03%20-%20Certified%20vs%20advisory%20data%20on%20Boeing%20Aircraft .pdf

[Breakthesilence]

The Runway tables we use don't show distances for landing performance for dispatch but only masses.

Those are the maximum masses to be used in order to comply with the factored landing distances for dispatch (Dry x 1.67, wet x 1.67 x 1.15).

So, if I'm flying to my destination and need to divert:

Dispatch method: I just have to check my landing mass and match it with the maximum mass of the table.

However, usually on dry runways we don't even check the landing distances because our few destinations have well suitable runways lengths.

In case of Wet conditions, it's the same..our destinations are still suitable up to the maximum landing mass.
Usually we fly to limiting airfield during summer and it's really difficult to find them wet (never had in 5 years flying there)

Regarding contaminated runways, we don't have specific runway tables. Our provider tells to use QRH data (so advisory landing distances...) :eek:
The problem is that we never fly to contaminated runways due to our network and location, but I think this is not something good to keep anyway.

[john_tullamarine]

A simple and, I think, more pragmatic approach is to consider the certification rule book stuff as having stood the test of time and representing sensible practice for routine operations and anytime you have the option of using the conservative data on the line.

If, on the other hand, things are getting uncomfortable with this and that failure, then the QRH stuff gives you some additional information which will provide some indication of where you might be able to recover but with a much lower probability of success.

Ergo, if you have the choice of going someplace which provides the normal factors then that ought to be an attractive option. On the other hand, if things are getting very uncomfortable one has to balance this risk against that and make the best call one sees at the time.

Where a problem arises, is the situation where one had lots of options available but ran with the first one which came to mind and ended up in the dirt off the end of the runway. Embarrassing and difficult to explain away, methinks ? Different matter, altogether, if you have few options with runways and were faced with a difficult situation.

[safetypee]

JS, thanks again for the additional info – IFALPA leaflet (#17).
This has the potential to be a valuable guide, but as with most aspects of aviation it is essential to know what assumptions or generalities are being made, and the limits of the referenced data.

The briefing leaflet and your comments on QRH data imply that certificated data is only used pre-flight. In practical terms this may be so, but the leaflet may over exaggerate the value of advisory data ‘en-route’ in normal operation.
Also, the use of revers thrust is overemphasized, see previous posts on reliability. Reverse thrust is a valuable safety feature. However, it is increasingly being used as the norm (must-have in order to stop), but in terms of landing risk (safety) this might not be justified; however it can recover adverse situations (nice-to-have if things go wrong).
Many pilots seek clarity between these alternative views. The regulations require specific margins for dispatch, but there are none for a pre-landing check (a check the FAA still only recommends).
EU OPS-1 is more specific – 'be safe'. This requires judgment, which requires knowledge and skilled application.

The IFALPA leaflet inadvertently encourages a ‘can we land’ attitude, whereas the alternative is ‘should we be landing’; if “yes”, then operators can consider how this can be achieved safely. The latter view requires good situation assessment and appropriate use of data.

Whilst flight test certificated data does not consider temp, slope, (CS 25.125); the presentation of this data in the AFM may show operational factors (CS AMC 25-1518).

The advisory ‘operational’ actual data has many assumptions. The most understated is the 1000ft airborne distance. Boeing quotes this for ‘small’ aircraft, but for larger aircraft this is 1250ft; thus the IFALPA leaflet is not generic. Furthermore, in-service data (research / FDM, FOQA) indicates that these distances are unrepresentative or normal operations (being much longer) and therefore a distance of Boeing 'actual + 15%' is more representative of what an accurate landing (with reverse and all else equal) might achieve.

The examples of spoiler / reverse effectiveness appropriately emphasise human error, but this emphasis overlooks other sources of failure / malfunction – ‘what if’.

The leaflet adds understanding, but the industry requires much more - clarity and simplicity as JT outlines above.

[PEI_3721]

A useful reference; a guide for judging what ‘factor’ to add to the landing distance in the pre landing check. http://www.superstructuregroup.com/Resources/Cathay_Pacific_TEM_Analysis.pdf