Do people use additional safety factors on the POH landing and take-off distances. The UK CAA recommends the use of "Public Transport" factors for private operations? This amounts to a factor of 1.43 on landing distance and 1.33 on take-off distance.
When I learned to fly my instructor implied that the POH values could only be achieved by test pilots in new airplanes and since most of us fly old airplanes and have skills somewhat below test pilot standard we should indeed apply the factors.....but do people actually use them?
[edited because I got the factors the wrong way around]
Anthony, I don't 'use them' in the sense of religiously apply them in an unthinking way. However, determing that your POH says today you should be at 50 feet, 1587 feet from the start off roll and then concluding that you're good to go because the 50 foot trees are at 1600 feet would clearly be a very bad call.
When I am going in and out of a 'tight' place, I look at the limiting case (am I dropping in over a hedge, or is there a large clearway so I can land near the numbers (the POH landing distance assumes you are at 50 feet over the threshold), on take off, am I worried about runway or climb out. I typically use unfactored 50 feet distance as my target for runway distance (however, when I do that, it is in the context of no significant trees and a slight dip away from past the end of the runway). My logic (flawed as it is) is that unfactored 50 feet is likely to be close to public transport factored 35 feet screen height (IIRC). If I was going out over the 50 foot trees in my initial example, I would use at least the public transport factors.
Typically in my aircraft (and with the approach clearways I experience), I can get into somewhere that I am not happy about getting back out of, so worry more about takeoff distance than landing distance.
I do when I have 4 people on board, regardless of how little fuel I might have, or I am landing on a 500m strip. I think some of the charts or graphs in the POH contain some margins, and then adding a load of additional safety factors might consider the flight to be look unsafe. The performance difference for wet grass, or a warm summer day really can make a difference so I prefer to be on the diligent side, and make a judgement on what I see. There are a number of iPad W&B or TORA apps which I use, though I double check against the POH sometimes.
I fly a C172 and I do so because it is very good for my average flight. There are times for example when I use a 250m grass strip with clear entry and exit lanes. If I had full tanks and 4 POB then I would not attempt this. I have the advantage of a private strip and from time to time check the T/O run needed, with a colleague on the ground doing the measuring. Better safe than sorry!
The proverbial "test pilot" who people think accomplished the remarkable feat of getting the "brand new" plane off in a stunningly short distance, and back on to a postage stamp, so the marketing department's performance number would look good, is a ways away from the real process.
Among the factors for aircraft certification is the frequent use of the term "must not require unusual pilot skill". The process for the determination is really rather conservative, and with a bit of attention to technique (what the flight manual said to do) and speeds, you might find you do better. There is better yet to be had in an emergency, but then safety margins are thinned, and more skill yet will be needed.
Short landings are really not that important if you want to reuse the plane, 'cause most will land and stop happily in less distance that they require to get back out. So, the successful landing into a tiny runway should put you on edge if you plan to fly out again, not be cause for self appreciation.
If the "old" plane you are flying, is not capable of the performance in the flight manual, you should probably having its airworthiness assessed. Yes, engines can be "tired", and they should be repaired, not flown with performance expectations. The 40 year old 172 with an airworthy engine should still do what the book* says it should.
One caution, I have found that for a few older Pipers, there was the commonly used "Pilot's Handbook", and a separate "FAA Approved Flight Manual". The Flight Manual did not give any performance data, and this was accurate. The "Pilot's Handbook" was suspiciously optimistic, and seemingly written by the marketing department, not the flight test guys. There was not a hope I could come close to those figures.
If you are planning to fly in and out of a runway as short as half again what the Flight Manual numbers state, you should ask yourself why you're doing that. There are few "good runways" which are really short for GA aircraft use. If you're headed into a short one, it might also have other challenges, like a less than idea surface or approaches. Give it thought as to how badly you need to be in there.
For water flying, where the body of water does not come with a stated length, I use Google Earth to measure it when I can do so in advance. I'll also fly practice approaches, noting approach and departure paths, and time the run over the useable surface to estimate length. But then on water there are extra trick possible too. Yesterday I was into a roundish lake for the first time. I had not wanted to overfly it, 'cause of the noise impact on a small town very close by. Once on the water, I realized that the trees all around were a little taller than they had seemed from above. No problem, I took off in a circle, and had lots of room. Indeed, the lake was more than twice as long as my minimum "comfort" takeoff distance for the plane, but that extra margin is always nice. And, the circular pat carried me away from town, so I hope I was neighbour friendly too!
I generally follow mm_flynn's approach.....and I have long suspected, as PilotDAR points out, that the intent of the charts is for the use of normally skilled pilots....but having being taught under a legacy British system (Singapore) the inference from my instructor was that the raw charts (drawn by those rash Americans) should never be used without significant factoring....it always seemed to me that most airfields which are short are grass and often on a slope....compound use of the factors often ends up with a requirement far in excess of the typical grass strip....and yes I note that it is take-off requirements that will dictate the minimum field length required
I do both. On commercial flights I am required to use factored distances (there is only a factor for the landing distance, not for takeoff however under JAR/EU/EASA OPS!). But we also do private flights for the owner with the same aircraft without the factor applied (otherwise we couldn't go where he wants to go...). It works the same. As Pilot DAR wrote, the figures from the manufacturer's books are conservative, Misters Piper, Cessna, Dassault, Boeing, Socata, EADS, Pilatus, .... are not particulairly fond of lawsuits. But I would never operate below the book figures other than in an emergency.
I don't apply factors, but I'm very cautious, taking temperature, ground condition, slope, and climb-out obstacles into account, as well as the likelyhood of carb icing on take-off and possible wind change. I could get in to a strip an eighth of what I'm happy to take off on. Cross wind limit depends on my currency in cross winds. As regards manual figures, our Jodel was a rebuild many years ago -its a 1960/65 model. I go by it's recent performance - it's prop is not in the manual. PS I hit the fence on an aborted T.O. 20 years ago.
I would not apply factors on top of the POH data (takeoff and landing performance), but I would be hugely cautious with grass for which there is no data and for which there cannot be much useful data because it can vary so much.
Once I went to a grass runway which was stated informally to be 1200m (Heywood Farm in SW UK) but it took me about 1000m to get airborne, because it was rough as hell and the ~20cm tall grass not only rubbished the takeoff performance (soft field takeoff notwithstanding) but also covered the whole plane with green crap which cost me £200 to get removed. I don't know how anybody can operate from such a "runway"; maybe a Maule with tundra tyres would be fine.
Some grass runways are fine. I used to fly to Panshanger which was OK.
All VP prop and turbocharged aircraft I flew could be flown to book values; my experience with fixed pitch prop is a lot worse on take-off performance, many did not make the static RPM so do not make book power. Not sure if this is a coincidence. An easy test is to compare en-route rate of climb with the book - if that performance is as per the book, the take-off performance should also be quite close.
However, the technique required to achieve the take-off performance can be hair-raising (Turbo Saratoga with stall warner blaring and nose so high you feel you are about to go vertical) or next-to-impossible to achieve without practice (T-tail Arrow, for example, need to visit the gym more often...)
Hence when I check out on an aircraft and practice short field take-off and landing, I use a GPS to compare the actually achieved values with the POH. At 1-second intervals, it is precise enough.
