AIRCRAFT PERFORMANCE

Acknowledgements: FAA GA Joint Steering Committee Safety Enhancement Topic

Accident investigations have discovered causal factors resulting from unreasonable expectations of aircraft performance – especially when operating at the edges of the aircraft weight and balance envelope. That’s why the Loss of Control Work Group suggests improvement in pilots’ understanding and calculation of aircraft performance. When we speak of aircraft performance we’re usually answering three basic questions:
·            How much can I carry?
·            How far can I go?
·            How long will it take me?
It sounds simple, but a specific set of interdependent variables must be considered in order to answer each of these questions. Most of these variables have to do with aircraft performance, but the greatest variable does not.

Weight and Balance
·    Decide how much weight you want to carry to what destination. If crew, passengers and cargo alone exceed your aircraft’s capability, make multiple trips or get a bigger aircraft.
·   Once you know your payload, you will know how much fuel you can take and that, together with your weather information, will tell you how far you can go. If you have enough to get to the destination plus alternate and reserve, great. If not, pre-plan an en-route fuel stop.

Take-off and Landing Distance
·  Consider your departure and arrival airports’ runway lengths, obstructions, and expected density altitude. If the field is short and/or obstructed you may not be able to safely fly with a full load.
·     Just because the book says the aircraft can do it doesn’t mean you can do it. Pilot skill and experience count for a lot, so be conservative when you calculate your performance. Some pilots add 50% to their take-off and landing calculations for safety.

The Greatest Variable … the pilot!
The POH figures and all of our calculations don’t mean much if we can’t duplicate them in our flying. That’s why it’s important to document your performance capability at least yearly with an Instructor.
·   In order to know what performance you and your flying machine are (or are not) capable of you’ll need to establish a baseline which co-relates pilot and aircraft performance under a given set of environmental circumstances on a given day.
·    Human factors such as fatigue and environmental factors such as higher density altitudes will result in performance below the baseline,
·    Proficiency training and lighter loading will likely result in above baseline performance.
·   The key point to remember is that for any given flight you need to pre-determine how you and your aircraft will perform.
·  To establish your baseline, load your aircraft with a typical mix of fuel, cargo, and passengers. (We recommend that one of those passengers be your Instructor.) Calculate your test weight and note runway condition, elevation, density altitude, wind direction and speed.
·   Also note what rotation and climb speeds you intend to use and calculate 70 % of the rotation speed. More on that later.
·    Fly several take-offs and landings noting your performance on each trial. When you’re done you can average your performance figures and complete your baseline chart.

Rules of Thumb for Take-off Distance
·   For a fixed pitch prop, add 15% to your calculated take-off distance for each 1,000 feet increase in density altitude up to 8,000 feet (12% per 1,000 feet up to 6,000 feet for constant speed prop).
·   When planning take-off from short unobstructed runways, establish a landmark at 50% of your calculated take-off distance. On the take-off roll you should have 70% of your rotation speed at that point. If you don’t, the safest thing to do is to abort the take-off.
·    If your plan can’t meet the above requirement, reduce weight or wait for more favourable wind and temperature conditions.
·    If you need to clear obstructions on take-off, you’ll need to have 70% of your rotation speed by the time you’ve travelled 30% of your available take-off distance.

Approach and Landing
You’ll want to be stabilised on final approach with full flaps at 1.3 times the stalling speed in landing configuration. Don’t cut your final short. Make it long enough to be stable and go around if you’re unstable.
FLY SAFE!
Tony Birth