The figures provided by the POH/AFM in terms of landing and takeoff distances are probably a good guideline in terms of one can expect. Are they however sufficient to ensure the safety of takeoff and landing?
The operator at which I recently trained for the IR-ME required to multiply all performance figures by 1.3 (except cruise speed 
). Since performance figures for flapless landings were not provided, the full flaps landing figures had to be multiplied by a factor of 1.6.
As a result the 1100 m runway at LFPN (Toussus) was not enough for a flapless landing under some circumstances (high weight, high temperature, low QNH).
In terms of safety you never have enough runway. Adding a fudge factor can save the day if you inadvertently land downwind, or did not take runway slope into account, or the runway happens to be (unexpectedly) wet.
What are the practices among members of this forum in this respect? Does adding such a margin make sense?
Since some owner/operators require such a margin, would it make sense to add this to the router’s performance section (default 1)?
Heresy to say this on EuroGA, but as far as I’m concerned (private pilot) such figures are a classic example of garbage-in, garbage-out. The garbage-in involves an arbitrary assumption as to the level of skill of a mythical “average” pilot. The reality is that at one end of the scale we see people like Breedon who can land and take off in one and a half Cub-lengths, while at the other we have those who steam in to Castle Kennedy at 1.4 Vso and (hopefully) go around after missing the runway threshold by two hundred metres. That is what they were taught to do at Prestwick or wherever. The same folk wait forever to lift the nose and then try to climb at Vx, when they could have lifted a foot or two off the runway 100 metres earlier and accelerated with minimal drag in low ground effect before trading speed for obstacle clearance.
Before landing anywhere where departure might be in doubt, we look for up- and down-draughts, and plan our exit so as to use or avoid them.
Thankfully there is no performance crap in any Maule flight manual, and if there was I surely wouldn’t lose sleep with an E6B trying to calculate whether I could safely depart Tignes or Verbier on a stinking hot day. I either see and feel it or I don’t, and if the latter, I need to burn another couple of thousand litres of 100LL in the circuit. And if I still don’t see it, the answer is “not today”, or perhaps, “not until this evening”.
I would ignore the 1.3 multiplier and concentrate on flying the correct landing speeds.
The one BIG caveat is grass, which can produce just about any result it feels like on the day. Also, at some “come to our BBQ at the strip – it’s really smooth” grass strips, your pilot performance may be impacted by multiple missing teeth 
The Maule (I have flown in one) can get airborne in the distance you can throw the towbar
The CAA has a good leaflet and I use it as my guide. Aircraft on public transport with approved flight manuals will typically have their performance charts already factored for PT operations.
https://www.caa.co.uk/docs/33/20130121SSL07.pdf
A PA18 had a PT AFM in the UK, not sure if at one point there was a PA18 on an AOC but presumably this prompted the CAA to Approve a manual. If I recall the LDR chart had some very un characteristic Super Cub requirements, of around 2,000’.
Like all things it is horses for courses. There are still plenty of regular GA mishaps on both takeoff and landing, where use of safety factors might have resulted in a better outcome.
The important criteria is really almost never the data in the POH or if the plane performs according to the POH tables. What’s much more important is that pilots use the right technique, develop a feeling for the airplane and its abilities and practices.
I don’t know how many 172s i have watched that had problems landing on our 900 m runway, ruining brakes and tires. But what do you expect if you land 500 m after the threshold with 80 knots? Many Mooney or Cirrus pillots will never land on a runway shorter than that, or would never go to places like Zell am See (LOWZ) with it’s 650 m runway, just because they are insecure and have never learned to properly control speed and to set up a stabilized approach.
Take-off or landing accidents very rarely happen because the perfomance of the a/c was too low, most times it’s the pilot’s performance that’s not adequate. One exception is overloading light planes, especially in the summer, and a CG outside the envelope. Those mistakes often result in deadly crashes.
Or let me put it differently: To what airfield can you you not go if you can perfectly handle a 172? Very few …
This is the Gross Unfactored Landing Distance Required from the PA-18-150 CAA approved flight manual. Using the PT safety factor of 1.43 a no wind sea level ISA landing at gross gives you a requirement of 2,500’ plus.
By way of contrast the Owners Manual suggests a landing roll of 385’. Albeit gross, not net, and no figure is given for landing over a 50’ fence.
Or let me put it differently: To what airfield can you you not go if you can perfectly handle a 172? Very few …
Flyer59 some of the Auster, Super Cub or Maule forumites might suggest thousands.
Flyer59 some of the Auster, Super Cub or Maule forumites might suggest thousands.
;-)
Twenty years ago i flew in a 400 hp Bush plane prototype called “Sherpa” over Orgeon’s Columbia River. Dense forest, a wide river. Over the intercom I hear Byron ask me “Are you ready for landing, Alexis”….. “uh …. I don’t see an airport, Byron”…. “I see hundreds, Alexis”.
We landed on the beach of a tiny island of the Columbia river … between tree stumps and rocks (I can post a picture later)
I think safety factors are essential, but need to be applied with some common sense, not “Public-transport-follow-the-rules” style.
For example, the really important one is take-off ROLL, and landing ROLL. In any environment where not achieving “book performance” leads to damage or death (e.g., runway end has a ditch or a cliff edge), not applying a safety factor is asking for trouble. The factors for take off distance are also very important because a few kts difference in lift-off speed from “book” makes a LOT of difference for the performance you get, and if you crash it will be at high speed so you ignore this at your peril.
The formal book landing distances are, however, a bit stupid on short fields, because they assume a 50ft threshold crossing and touching down 300m into the runway, plus factoring that means you need 425 m runway before the (factored) landing roll starts. So basically unless you can stop in the remaining 100 metres or so, you would never fly anything in Aachen-Merzbruck (520 m), a place where Senecas and Mooneys happily depart and land, because everybody touches down on or right after the “piano keys”.
Of course, in private ops you decide what factor to use – your funeral, as they say. If you are comfortable with ending up in a bit of grass and a red face on a field you know, go ahead.
Personally – if I go to a field where I cannot achieve factored take-off roll, factored take-off distance, or factored landing roll from the expected sensible touch-down point, I probably won’t go. If I can’t achieve factored landing distance, I do some homework on where I can expect to touch down before I decide (VFR). IFR, I assume touchdown in the TDZ, but runways tend to be long enough anyway at these airports.
RobertL18C wrote:
The CAA has a good leaflet and I use it as my guide.
You must be operating your Cub out of Heathrow with minimum fuel, then.
Coming up with bounds (like the leaflet does) is easy. Coming out with tight bounds is hard, but loose bounds are useless…
RobertL18C wrote:
There are still plenty of regular GA mishaps on both takeoff and landing, where use of safety factors might have resulted in a better outcome.
If they used those factors, they’d given up flying, so yes, it would have resulted in a better outcome
For example, the really important one is take-off ROLL, and landing ROLL.
That depends on the aircraft. In the PA28 take-off roll is almost never a problem, what’s potentially killing you is take-off 50ft distance
