Public Transport Landing Factor

[dawsonj1]

Something was brought to my attention when converting onto a new type earlier this year that the 1.43 public transport safety factor is only relevant at the planning stage. Once airborne this goes out the window so to speak and you no longer need to apply it.

My question is why can we disregard this once airborne? I get the point that you may have to be more flexible when airborne due changing circumstances, abnormal procedures etc but that's the case with many other things too and why we can operate outside of SOP's when it can be justified of course. Maybe I'm over thinking it and should just accept it as it is but just wondered if anybody else has any ideas on this performance subject?

[FlyingStone]

My explanation would be that the 1,43 factor (requirement to land within 60% of LDA) is because in planning phase you only take the forecasted weather conditions into account. And even if forecasted weather turns out to be more optimistic than the actual weather, you will probably still end up with some margin in the landing distance.

It is also to prevent cowboys from scheduling a flight into (too) short fields. If you take off, you have to land somewhere, but scheduling a flight with minimal (15% or even lower) margin to LDA would be very stupid.

[safetypee]

dj1, there have been several discussions on this subject for commercial operations in tech log.
The central issue is the justifiable level of safety.

The pre takeoff factored landing distance could be discarded in flight if there is an alternative means of calculating landing distance, and one which provides a similar level of safety as the pre takeoff calculation. This probably means adding a factor according to the circumstances, but a factor on to what baseline distance.

Many commercial operations did not use the standard factors and substituted their own methods in flight. Unfortunately they often used manufacturers’ actual distances as the baseline which differed considerably (no factor or margin depending on assumptions) from the certificated performance in AFM, which is the basis for the pre take of factors.

Recently commercial manufactures have published much more realistic ‘actual’ operational landing data, often with a minimum factor of 1.15, but even with this the responsibility for the safety of the operation resides with the operator who is expected to add further margin as judged before landing.

For public transport ops it might be easier to use the pre takeoff factor in flight as the basis of your justification, which should additionally consider any in-flight changes and the actual conditions before landing.

[john_tullamarine]

My explanation would be that the 1,43 factor (requirement to land within 60% of LDA)

Perhaps you might like to recheck that sum just once more .... ?


While there will be variations between Contracting States, and between the various historical evolutionary versions of the Design Standards (as with all things) the deal for heavies usually seen is along the lines of ..

(a) planned requirement 1.67

(b) alternate requirement 1.43

A problem is that many AFM landing charts are not factored and you need to add the fat yourself.

Some things to consider -

(a) actual screen location - ie are you high ?

(b) float distance - have you ever seen what the usual performance landing flight tests are like ?

(c) have you ever practised max performance landings ? - a whole different ballgame to line operations

(d) you think you can replicate the AFM raw data on the day ? .. pipe dream. That's one of the reasons for the factor fat.

(e) actual runway surface conditions - ie friction characteristics - especially as you start skating on the upwind touchdown zone deposits with maximum braking ... and, if it's wet/contaminated, you might spoil your whole day, big time.

Keep in mind - always - what your story might be in court after the prang when you skated off the end of the runway and a bunch of folks get hurt or killed. If you had no reasonably feasible alternative, including planning considerations, then you may have a winnable argument for shaving the fat as circumstances required on the day.

If, however, you chose to land on a shorter runway, with another available with lots of length ... rather you be the one in the witness box than me ...

[c100driver]

The international arm of the Airline Pilots Assn published a great discussion document that uses pilot language to explain your question.

http://www.ifalpa.org/downloads/Level1/Briefing%20Leaflets/Aircraft%20Design%20&%20Operation/12ADOBL03%20-%20Certified%20vs%20advisory%20data%20on%20Boeing%20aircraft .pdf

[dawsonj1]

Thanks for your replies guys.