Perhaps a strange question from a Maule driver (cos there ain’t none 
) but, prompted by a thread in the Bizjet section, I wonder:
Peter.
Jacko wrote:
Does your POH include figures for landing, take-off or cruise performance?
If so, do you trust them, or do you add some kind of “Jesus factor”?
If you have checked them, are they accurate for your piloting technique in your particular aircraft?
Do you think that the utility of such figures outweighs their real-world flaws and disadvangages?
Yes, my POHs do (PA28-181 and C172S), and at least the cruise performance figure are surprisingly accurate. Take-off performance appears accurate too, but of course I don’t really know my exact height over the departure end of the runway. Swedish regulations require me to add a 43% safety margin to landing distances so I have never had reason to check the book figures for correctness… (I can’t wait until part-NCO!)
I have found the cruise figures in the POH of the C172b to be quite exact, too. Of the MS894A not so much, but then we did add a Gomolzig silencer and a Hoffman three blade prop. The DR250 seems to be accurate, too, within a tolerance of 2% or so.
For take offs, I always add around 50% “albatross factor” on the book value. Other than in the DR250, we don’t have problems with the landing distance, if take off is possible. That gives the comfort of being able to depart anywhere I can land in our DR250. But you have to follow book procedures to get close to book values, that is true. I would like to test these values, but the test setup isn’t that easy for takeoff or landing distance. Takeoff roll and landing roll are much easier to determine.
Does your POH include figures for landing, take-off or cruise performance?
Yes (C150/2, C172, PA28(R), Mooney M20J, PA32R, Bonanza V35, DA40, Columbia 400, SR22TN, C303, DA42)
If so, do you trust them, or do you add some kind of “Jesus factor”?
I found them quite accurate; even in very old aircraft, the only time there were major discrepancies there was something wrong with the aircraft.
I do not trust them for marginal cases unless I have flown them myself and am current / comfortable. By marginal I mean anything with less than the safety factors applied, and am much more cautious about take off performance than landing, since a marginal overrun on landing means embarrassment and bent metal, while an overrun on take-of happens at much higher speed and can result in death.
Whenever I fly a performance departure or landing, I check afterwards expectation vs. actual – I fly out of Biggin, so A3 is a very useful benchmark for testing this. I regularly fly take-offs and landing treating the turn-off as runway end. Haven’t made the C303 stop by A2 yet in the C303 for consideration of the brakes and ATC health (heart-attack prevention), though.
If you have checked them, are they accurate for your piloting technique in your particular aircraft?
As said elsewhere – you need to fly the technique, which varies considerable between aircraft. Especially take-off technique for performance can be very uncomfortable, and older aircraft (pre 50-ft-3-degree-area) have interesting performance landing techniques.On the flip-side, Also, in many aircraft landing distance (NOT landing roll) can easily be overachieved with steeper approaches or earlier touch-down.
My checklists (posted elsewhere) have a little weight – speed table for performance take-off and approaches to get them right.
Do you think that the utility of such figures outweighs their real-world flaws and disadvangages?
Yes.
Ah, yes – while many instructors frown at the idea of a “rotate” speed for light aircraft, my experience is that in higher power ones (in particular the PA32 and the C303) you really need to heave back quite a bit at the right speed, our you will not nail the lift-off and initial climb speeds, be too fast and too low. Sometimes the speed that you need to start lifting the nose is in the “small print” of the technique, or at the bottom of the performance chart.
If your aircraft type has been used for public transport it should have a CAA approved flight manual, in addition to AOC type operation manuals. All these will be safety factored trying to achieve the 1:1million accident standard, or better – although for Class B aircraft this is probably unattainable.
These manuals are much more conservative than the manufacturer’s POH, in particular for take off, landing, balked landing, NTOFP, drift down, service ceiling, flight planning block speeds and endurance planning.
If we flew our GA aircraft to AOC/PT standards our accident rate would be one tenth of what it is. Using public transport safety factors for performance calculations is a meaningful way of achieving this.
However, this can be taken to somewhat interesting levels of caution. The CAA AFM for the Super Cub shows a LDR of 1,800 feet, while the POH suggests a somewhat spuriously precise landing run of 385 feet. Albeit the former is over the 50 foot barrier, while the POH is landing run only.
RobertL18C wrote:
The CAA AFM for the Super Cub shows a LDR of 1,800 feet, while the POH suggests a somewhat spuriously precise landing run of 385 feet. Albeit the former is over the 50 foot barrier, while the POH is landing run only.
Would the CAA AFM be available anywhere? I would be interested to see it. All I have is a POH from the internet for a 1976 model (which is the same year as mine)
Neil you can find it on supercub.org. To add insult to injury the CAA classified the cub as Performance Class D under the old system (we only have A and B, with some vintage airliners as C).
Wow. 550 meters for a cub. Belts, braces, superglue AND holding it up with both hands.
Fair enough – 300 metres of that is the 3 degree glide from 50ft down to the runway. Anyone who lands halfway down a short runway should get points on their pilot licence.
