Landing Performance

[Ocampo]

So...here I am, reading my notes about performance, and came across something that I am yet to understand.

Limitations for Landing Weight are Runway Length, Approach Climb and Landing Climb.

Runway length, takes into account: Dry runway, Maximum manual braking, "positive" touchdown, speed brakes in use and no reverse, and states the following: "TCH 50', measured from TCH, runway length limitation is demostrated CD (certified distance) + 67%"

What's the 67% used for?

[Max Angle]

It's the safety factor that is applied to the basic performance to get the length that is required for normal operations. The rules (EU-ops and FAA I think) say you must be able to complete the landing using only 60% of the available runway which is the same as saying that your required length is the actual demonstrated distance plus 67% (*1.67). Wet runway requires *1.92

[MU3001A]

Certification requirements. Transport category aircraft are required to be able to land within 60% of available runway length. Actual landing distance x 1.67 = overall runway length needed to comply with this requirement.

[Mad (Flt) Scientist]

Just to note that the 60%/67% factor applies only to planned operations. Once you are en route, changes to circumstances 9weather, aircraft failures, runway availability) may mean you don't have the margin available any more, which is acceptable - indeed, it's the whole point of the margin in planning, to account for these circumstances.

Its not a Transport Category aircraft requirement - there's nothing in Part 25 about a 60% factor. It's only alluded to in 25.1587(b)(7). The factor (and it's also not always 60%) is in for example 121.195(b). It's an operational requirement only.

[hetfield]

@Mad

Fully agree.

BTW our SOP require to mention landing performance during approach briefing.

So, now it's inflight....what to brief?

- actual or
- required ldg distance....

regrards

[mcdhu]

As I understand it - and I probably don't - it's 'actual' that you now consider (in the air). The FAA mandate a 'factor' of an additional 15% which Europe has yet to embrace, but it's a cracking idea!

It's probably time for Old Smokey, JT or one of the other 'professors' to come in.

Regards all
mcdhu

[gearpins]

+67% is a despatch requirement. In flight if proceeding to planned destination and no a/c system degredation,then landing perfomance would not be an issue.
If enroute any a/c system degradation leading to higher Vapp or stopping capablity occurs then actual landing distance needs to be calculated-
ALD+CORRECTIONS(for the failure,wind,pressure alt etc)=CORRECTED LANDING DISTANCE.
In theory this should be enough to land and stop.Faa insists on adding 15% to this as a safety margin
I agree:bored:

[Ocampo]

Thanks to everybody for the quick replies.

However, to gearpins, I find it quite hard to go and search for the Landing Performance or Landing Ground Roll charts on the manual if I have a serious failure situation going on. To tell you all the truth, when I am on a sim session and a flight divertion needs to be executed, (if I am not flying on a area I know) I just look for the approach chart and look for the category of my aircraft, if I found it, good enough, if I don't, then search another airport (which I should have a some 3 or 4 in my mind already before taking off since I did a planned my flight).

Adding a little spin, yet still talking about performance, only this time it would be takeoff performance, I found something else. Goes like this:

"If SWY is larger than the CWY, V1 is increased. If CWY is larger than the SWY, V1 is decreased".

I assume that is because you have the additional "runway" surface to stop, in the event of a RTO. However, I don't understand what's the point of stating the CWY in that sentence, or what role does it play. (Oh, boy...I'm too ignorant! :O )

[john_tullamarine]

When we are talking about certification performance landing trials we are talking about TP finesse .. which is not the sort of finesse the line pilot might aspire to day in, day out.

Probably the most alarming (if not outright frightening) experience I've had was the first time in the back on such trials. It would have been nice had the boys briefed me beforehand ... c'est la vie.

TPs are not paid to do smooth landings which the little old grey headed grandmother in row 25 will think "that was nice, dear" .. they are paid to get numbers .. good numbers.

Maximum manual braking better believe it.

"positive" touchdown been more than the odd aeroplane broken in half during such touchdowns

no reverse doesn't make a whole lot of difference on a dry runway

runway length limitation is demonstrated CD (certified distance) + 67%"

You and I will NOT achieve the TP's data unless the Gods are smiling broadly on the day and we are VERY lucky.

Not even the TP will achieve his/her own book figures every time.

In the real world, the TP does his/her best to get the shortest distances he/she can. If he/she doesn't like the particular test point result .. read "I really could have done better on that one", he/she scraps that result.

Once the TP has done his/her bit, the aerodynamicists look at the test set and throw out a few more "not quite right" results.

The end data set (considered to be "good") then is put up to the Regulator for assessment.

Unfactored book figures should be viewed as being the absolute shortest distances achievable in the best circumstances with a bit of luck thrown in for good measure... ie a brick wall limiting figure

So, now it's inflight....what to brief?

- actual or
- required ldg distance....

It follows that, on the line, generally you WON'T achieve the book figure. You might not pass that distance (read "go off the end of the runway") at breakneck speed but you can reasonably anticipate going off the end to some extent. It is important to keep in mind that the speed decay characteristic curve under heavy deceleration is quite steep .. so a small distance error translates to a potentially high speed excursion .. high energy .. high damage .. front page in the local newspapers.

If you have an inflight problem impacting on landing distance, that just has to be incorporated into your overall risk assessment when figuring out just how you intend to recover the aircraft.

The level of pilot interest ought to relate to the margin on the day ..

If you have only the one runway available and it's VERY marginal, then tough luck .. you do the best you can on the day. .. and you will be very interesting in briefing the landing (and subsequent emergency services action) on the day

As the margin increases, you can relax progressively.

If you have several runways then, as PART of your flight management risk assessment, you might prioritise the runways on the basis of length. Not suggesting that the only consideration is runway length and anticipated pad factor .. but it is an important one to consider.

The end result, looking at certification and operational rules - you don't use minimum length runways as that would be an unsuccessful career and, potentially, life, strategy.

The factors mandated vary across rule sets but are intended to provide some fat for all the "normal" things which might conspire to bring you unstuck on a particular landing. Distance/0.6 (= distance x 1.67) is the factor normally applied for heavy aeroplanes.

it's 'actual' that you now consider (in the air).

I suggest in terms of the sorts of concerns listed above.

Faa insists on adding 15% to this as a safety margin

If that's all I had on heavy metal, I'd be sweating heavily during the approach ...

I just look for the approach chart and look for the category of my aircraft

The sort of training paradigms to which I was exposed had us knowing what set of available runways were reasonably available for every flight .. preflight. Always seemed to be a sound sort of insurance gameplan to me.

If SWY is larger than the CWY, V1 is increased. If CWY is larger than the SWY, V1 is decreased

Can't say that I can bring to mind any circumstance in which stopway would be longer than clearway .. do you have any examples you can cite ?

Main idea here is that the extra TODA bestowed by the clearway allows you to unbalance the takeoff (a bit more) with a lower V1 to achieve a shorter ASDA and a longer TODR. In practice the statement is just another way of saying we like to optimise the takeoff.

Keep in mind that, just because the airport authority gives you various values for distances .. your particular aircraft will not be able to use all the distance for each measure .. one will end up being limiting for the particular calculation.

[Ocampo]

Can't say that I can bring to mind any circumstance in which stopway would be longer than clearway .. do you have any examples you can cite ?


Actually, no. I think it's (like most of these things) theoretical.

Keep in mind that, just because the airport authority gives you various values for distances... your particular aircraft will not be able to use all the distance for each measure .. one will end up being limiting for the particular calculation.

Point taken, sir. Quite an interesting reading about the test pilots.

[planett]

Quote
"Can't say that I can bring to mind any circumstance in which stopway would be longer than clearway .. do you have any examples you can cite ?"

CYGO Gods Lake Narrows Manitoba Canada.

Independant survey beyond airport operators declared distances (but approved for company use) Shows RWY 14 stopway and clearway available about 1100' while clearway credit in Canada maximum 1000' beyond threshold.

Moot point since most aircraft are limited by the rather short TORA. (unless waived by the gravel operations)

Believe me, certification landings are a regular occurrence here.

[john_tullamarine]

Independant survey beyond airport operators declared distances (but approved for company use) Shows RWY 14 stopway and clearway available about 1100' while clearway credit in Canada maximum 1000' beyond threshold

Interesting. However, the airport declared distances were the bit in question.

Can you offer comment re the 1000ft limit .. that is needlessly limiting in the real world. Is that a general local regulatory limit (and that's fine) or is there something about this particular runway that presents some rational reason for a specific limit for the case ?

[planett]

The survey allowed more, it was up to the operators to regulate themselves to the Transport Canada 1000' clearway maximum, where no such limit exists on stopway. (Buried in the CAR's somewhere I can't find now..............Listening to Space 1999 soundtrack)

[safetypee]

MFS Re “… the 60%/67% factor applies only to planned operations. Once you are en route, changes to circumstances (weather, aircraft failures, runway availability) may mean you don't have the margin available any more, which is acceptable - indeed, it's the whole point of the margin in planning, to account for these circumstances.”

This doesn’t appear to be the interpretation of the UK CAA – Large Transport Aeroplanes - Landing Performance (www.nats-uk.ead-it.com/aip/current/aic/pink/EG_Circ_2006_P_014_en.pdf) paras 2.3, 2.4, & 7.1, 7.2.

The inference in the AIC (assumptions) is that in normal circumstances, an in-flight reassessment should aim to keep the same margin of safety as calculated before take off.

The 60 – 67% factor is not a margin of safety as implied by some; it is a ‘field length factor’ for determining the landing distance required(LDA), which provides an excess distance over the theoretical minimum; this margin provides an acceptable level of safety in normal operations.
In ideal conditions the margin (40% excess) is unlikely to be achieved even when considering the variables which the pilot can control (speed, touchdown position). The unknown factors and error in reporting (runway texture, rubber deposits, wind strength), further reduce the margin of safety.

When landing on a wet runway, the margin, probably already a smaller % distance than dry, is also reduced by ‘unknowns’, e.g. depth of water, surface composition, or other contaminants (rubber, dirt, paint). These reductions are judged as acceptable up to the boundary of ‘flooded’ or ‘contaminated’ depth of water (3 mm, 1/4 in), i.e. the ‘normal’ margin of safety is reduced, but is judged (by the regulations) acceptable although in practice it might be a very small distance. However, the hidden assumptions in deteriorating wet conditions might include mitigation of the risks with close attention to touchdown speed (and wind), touchdown position, and braking level.

The FAA view in AC 91-79 (www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/0052f2a2a00d91b28625738e0071e44c/$FILE/AC_91_79.pdf) is similar to the UK AIC, but with some ambiguities.
A particular point of interest is that the FAA ‘15%’ additive “is intended only to account for slight variations in achieved performance” (para 6) and thus crews might have to consider other risk-increasing variables – runway surface type, texture, depth of water, tyre tread, contaminants (dirt, dust, rubber,) in their calculation of LDR. Note the preceding text in Para 6 d (2).
The example in Table 3 shows how a nominal 3000 ft can become 5660 ft dry before adding a wet factor (I don’t think that this 15% is necessarily the same 15% as elsewhere in para 6).

Similarly, it is not clear how the manufacturers’ recommended approach and landing speeds above Vref should be accounted for. Some may ‘hide’ the excess (500ft/10kts) in the safety margin, thus further reducing the 15% ‘margin’, whilst others adjust the distance to retain some safety margin.

For in-flight assessment, some manufacturers publish advisory data which includes the use of reverse thrust; this from the experience of normal operations might give a false sense of security – certification may not give any credit for reverse due to it’s ‘availability’.

With in-flight failures, it may be possible to reduce the safety margin. This suggests that first you know what the normal margin is, what the changes could be, and hence how much it can be changed. Second, the crew have to ensure that any mitigation of the increased risk (accurate Vref, ‘short’ touchdown, max reverse) will be achieved – if not, go around: are you always able to GA with the failure?

Landing is a ‘risky’ operation. Justification of the decision should be supported by the best possible knowledge of landing operations, e.g. how the certificated performance is obtained, what the dispatch requirements mean, what assumptions are associated with published performance, and what the safety factors may/may not consider.
There are many other practical aspects relating to a particular situation, requiring good situation assessment.
Also, have some scepticism about what is reported about the runway condition and the braking action; beware of PIREPS.

IMHO, aiming to have the factors required for dispatch would provide a reasonable safety margin. The better option is to ‘know before you go’, and thus for unforeseen in-flight circumstances pilots might wish to prepare a quick reference guide to landing performance for a range of general conditions.

Managing Threats and Errors During Approach and Landing. (www.flightsafety.org/ppt/managing_threat.ppt)

Flight Safety Foundation ALAR Additional Resources (http://www.flightsafety.org/alar_resources.html) chapters 7 & 8.

Running out of runway. (www.nlr-atsi.com/downloads/NLR-TP-2005-498.pdf)

[PEI_3721]

mcdhu “ … it's 'actual' that you now consider (in the air). The FAA mandate a 'factor' of an additional 15% which Europe has yet to embrace, …”

IIRC the FAA mandating action (post Midway accident) was deferred, all that exists is the recommendation for “Landing Performance Assessments at Time of Arrival (Turbojets)” (http://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo/all_safos/media/2006/safo06012.pdf) in SAFO06012.
Is this ‘recommendation still ‘live’; what’s the current position with FAA rulemaking?

Europe on the other hand has had a mandate to use contaminated landing data in JAR/EU Ops for some time, which includes a 15% margin. Perhaps the FAA are still in catch-up mode.

[hawk37]

Mr JT, you said:

"Once the TP has done his/her bit, the aerodynamicists look at the test set and throw out a few more "not quite right" results."

can you give us some examples of what would be considered "not quite right"?

too slow, or too steep at the 50 foot point?

[john_tullamarine]

(caveat - based on my observations and experience from a previous life)

Considerations

(a) you need a sufficient sample size to satisfy the Regulator as to validity

(b) subject to (a), you might discard "spare" runs.

Off speed, as you cite, would be good starting point for cause. Gradient didn't appear to be a significant problem .. such trials are done in good wx conditions and the TP generally runs a good gradient to the 50ft point.

At the end of the day, the Regulator has to be satisfied that the data set is reasonable and representative .. but, within that, the OEM is going to skew the set to the low side of the distance distribution to the extent one can get away with ...

Generally the crew will discard off target handling runs while the engineers will be looking more in a global sense to skew towards the low side while preserving a sufficient sample size.

The D/0.6 captures this variation such that the line pilot doesn't have to worry too much, providing that he/she doesn't waste runway for those cases where the available approximates the required.

I am particularly concerned, however, by those who appear to have a belief that using QRH unfactored minimum data is a good strategy.

If that's all you have available to you, fine .. but expect to go off the end in the real world on most occasions if you are on speed and on slope. While you might toy with the idea of coming in below speed and below slope, such strategies come with a new set of problems .. and you are generally better served to go off the end at a lower speed than crash on the approach at whatever speed ..

In all cases, the WHOLE picture needs to be examined and a global assessment of strategy made .. runway distance is just one part of the jigsaw. There is not much point focussing in on one aspect of the solution and then get clobbered by something out of left field that you didn't bother to consider.

In my view, the line pilot's pucker factor should start rising as soon as we go below 1.67 and increase exponentially as the (actual) available factor reduces further ...

[AirRabbit]

In addition to all the good points made about what the test chaps do during certification flights is the line pilot’s understanding of several things: energy on short final (mass and speed); touchdown distance down the runway; the importance of quickly getting all the weight on the wheels; seat position relative to the controls (particularly, to the brake pedals); the position of feet on those brake pedals at touchdown; just how far those brake pedals have to be depressed to approach a max braking effect … and, in inclement weather, the necessity of getting all operating engines into maximum and symmetrical reverse thrust. Test pilots are used to all of this as a “day-in and day-out” routine. Typical line pilots are not.

Some time ago we had a discussion of feet position on the rudder pedals during takeoff – but it’s even more important here, because you’re going to land at some point after each takeoff, while (we all hope) you aren’t necessarily going to reject every takeoff. How many times have you seen the pilot, when asked to “set the parking brake,” have to adjust either the seat or his/her position in that seat in order to depress the brake pedals far enough to engage the parking brake? That is at least as far as those pedals will have to be depressed to get close to maximum energy braking. If your feet aren’t positioned to get the maximum mechanical advantage, you won’t get maximum pedal deflection – unless you regularly bench press a small car with your feet. And the seat position is important in the event you have to maintain directional control aerodynamically with the rudder WHILE depressing the brake pedals to their maximum extent!

[salamanderpress]

What a really interesting thread.

Just like to add. Stopway can exceed clearway because while the piece of ground meets the width required for use as stopway, it doesn't meet the increased width required for clearway, f'rinstance a hillock off to the side which is safe to ROLL past but not to FLY past. (Without considering the lateral dimension, it sounds mystifying that you can roll on it but cant fly over it...!)

[Sir George Cayley]

In all of this just remember (and I'm beginning to bore myself) that the amount of runway behind you at the point of touchdown is of no use whatsoever.

In other words, stabilised on approach at the right Vref is good.

In other, other words a good landing comes from a good approach.

And Stopways? Is grass OK?

Sir George Cayley

[DFC]

And Stopways? Is grass OK?



Stopways only apply to the accelerate - stop case. They are not included in the LDA.

Grass is OK for a stopway when the aircraft for which it is intended can use grass and it is maintained to the required standard.

i.e. in general a grass stopway would for example be OK for say a Kingair (certified to operate from grass) but not for a citation (prohibited from operating from grass).

I would caution against using the unfactored flight manual data for landing in anything other than a "Land Immediately" situation - eg uncontained fire, smoke in the cockpit or similar. In these situations the high probability of an over-run is easily balanced by the urgent requirement to get back on the ground.

Any other reason for return or diversion could not justify the high risk of an over-run and therefore appropriate factors including those applicable to overspeed at the threshold need to be applied.

Regards,

DFC

[Ocampo]

Stopways only apply to the accelerate - stop case. They are not included in the LDA.

Really? I thought they were used for "aircraft on landing roll-out, taxi and departure" :confused:

[ClimbSequence]

Really? I thought they were used for "aircraft on landing roll-out, taxi and departure" http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/confused.gif

Probably you are confused with a Displaced threshold:ok:

[Ocampo]

Probably you are confused with a Displaced thresholdhttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif

Which can is "a sort of" stopway, right?

Thanks for the reply.