landing distance and runway required

[Bungfai]

From my company manual, landing distance is 60 percent of runway required. Then before making an approach, I have to check if the available runway is at least equal to or longer than runway equired. But some folks here said it is only for planning. For actual flight, only have to compare to landing distance not runway required.It is OK to land on the runway which has the lenght that equal to or longaer than landing distance. Any of you have any suggestions on this. Thank you.

[hetfield]

Unless you are a superb test-pilot, touching down with the brake pedals depressed and exactly with Vref and some other factors you better use the landing distance required.

[safetypee]

Bungfai, there appears to be two differing views, either from Europe (JAR-OPS1), or the USA (FARs).
Both require factored distances in planning (for dispatch).
JAR-OPS maintains the factor for the flight, during which the Captain should reassess the landing conditions and if necessary readjust the landing distance required, i.e. increase distance if adverse conditions are encountered, dry factored to wet factored, or wet factored to contaminated (new data).
FAR does not require the Captain reassess the landing distance before landing and in flight operators can apply their own data (less than 60% factor), often with many (hidden) assumptions. See NTSB Midway (http://ntsb.gov/Recs/letters/2007/A07_58_64.pdf).The FAA now recommends a pre landing assessment adding a distance margin. This is not mandated and in theory a landing could still be conducted with distances much less than the 60% safety factor.

From a safety view, JAR has advantages in reducing the possibility of crew error or misjudgement of the conditions (or personal bias).
AIC P_014 (www.nats-uk.ead-it.com/aip/current/aic/pink/EG_Circ_2006_P_014_en.pdf), explains “the safety 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”. Also that the unfactored distance “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”.

AC 91 (www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/0052F2A2A00D91B28625738E0071E44C?OpenDocument&Highlight=ac%2091-79) and Landing Threats (www.flightsafety.org/ppt/managing_threat.ppt) provide estimates of the additional distances which should be expected for errors in the approach and landing accuracy. Any combination of these will increase the landing distance required above the unfactored distance. Considering other variables such as the runway surface condition, accuracy of wind measurement, and braking action, then in total there might be little difference between a sensible additional margin over an unfactored distance (FAR) and the calculated safety factor (JAR).

In some adverse circumstances the 60% safety factor (1.67) might have to be increased to 2.2 or 2.4 to achieve the same level of safety experienced in dry conditions see 14273E. (www.tc.gc.ca/tdc/summary/14200/14273e.htm )

Considering the recent high number of overrun accidents, I suggest that where there is a choice, the larger safety factor be used, and in adverse conditions provide additional safety margin with distance and/or procedures e.g. no tailwind.

[Checkboard]

Actually, JAR-OPS 1.475 states:

(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, allowing for expected reductions in mass as the flight proceeds, and for such fuel jettisoning provided for in the particular requirement.

[john_tullamarine]

A more pragmatic approach ..

(a) unless there is a REALLY important reason .. plan and use runways which give you the certification factors

(b) if you are caught out with a problem and, say, have to divert, then assess the available runways - prioritise the runways in the normal manner but include a consideration to capture distance factors as well as all the other things which one would consider

(c) if you are landing on a runway with the certification factor, or better, it is reasonable to anticipate a straightforward exercise

(d) if landing with less than the full factor ... as the factor decreases, anticipate an increasing probability of an overrun

(e) if landing with less than the basic figure, plan on a significant overrun

Anything else is probably a tad optimistic ...

[donstim]

JAR-OPS maintains the factor for the flight, during which the Captain should reassess the landing conditions and if necessary readjust the landing distance required, i.e. increase distance if adverse conditions are encountered, dry factored to wet factored, or wet factored to contaminated (new data).

Safetypee, could you cite the specific JAR-OPS 1 reg that maintains the safety factor for the flight?

JAR-OPS 1.400 requires commander to satisfy himself prior to commencing an approach to land, that a safe approach and landing can be
made, taking into account the actual state of the aerodrome. But it does not specify that the factor used for dispatch remains applicable.

Thanks

[pipertommy]

Hi, Sorry for jumping in with a question but this 1.67 AND 1.92 WET factor has always confused me slighly! Why not just 1.60 factor as its 60% DRY thats required for a jet. I remember from the groundschool something like LDR X 60/100 being turned round with 100/60 = 1.67 x LDR
Why not just use 1.60?

[safetypee]

donstim, my view is based on the absence of any specific requirement enabling changes in data which reduces landing distance factors before landing, together with the interpretation of a ‘safe approach and landing’.

I recall a distant view of French certification (Pre JAR/CS) that might have influenced European thoughts; - “… everything which is not specifically authorized is prohibited ”.

The landing distance references are in JAR 1.510 onwards, which also refer back to 1.470 (as in # 4). I understand that the distances referred to in 1.510 are those given in the AFM.
For JAR (CS) certified aircraft the AFM landing data already includes the distance factors (CS 25.125 [FAR similar], 25.1587 AFM requirements, 25.1591 contaminated data.
Although JAR 1.400 refers to landing data in the Ops Manual, I don’t recall any JAR operator having an Ops Manual (or computed data) which differed from the AFM, although there may be specially authorised exceptions and of course abnormal/emergency operation.
I think the latter point is the main difference between JAR and FAR operations.

[roljoe]

Hi,

your actual landing distance should be equal or less than 60% of the landing distance available (dry conditions).

You have 2 way to veryfy it, you take the available landing distance, consider 60% of it, and your actual landing distance should be less or max equal...

Another way is to multiply your actual landing distance by 1.67, and this distance should be equal (max) or less than the landing distance available.

Hope it helps...;)

[john_tullamarine]

your actual landing distance should be equal or less than 60% of the landing distance available

If the LDS is roughly that required by the AFM for the conditions ... then the first part of your statement is dangerously optimistic .. a more reasonable view is that your actual landing distance (if you're lucky) might be somewhere near (but probably somewhat above) the 60% value ... but only if you effect something approximating a flight test performance landing .. which the average line pilot without any FT background is not going to achieve.

That is to say, unfactored AFM LDR should be viewed by the line pilot as a not-quite-achievable wishlist item ...

[LA931]

Does anyone know which FAR states that the actual landing distance has to be 60% of the required landing distance?
I just read FAR 25.125 "Landing-Transport Category Airplanes" and it doesn't say anything about it.

[tribo]

Have a look at this link:

Regulation of Fractional Aircraft Ownership Programs and On-Demand Operations (http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgFinalRule.nsf/0/f3b9c464b4a88a6b86256daa00574821?OpenDocument&ExpandSection=6)

[LA931]

I just answered my own question.

FAR 121.195