October 01, 2012
By Fred Georgefred_george@aviationweek.com
Approved aircraft flight manuals are chock full of precision airport performance data, numbers obtained by some of the aviation industry's most skilled and experienced test pilots. These data have been thoroughly verified and validated by airworthiness certification authorities to assure they accurately reflect the ideal performance capabilities of the aircraft under certain conditions specified by government authorities.
Both FAR Part 25 and EASA CS-25 state that the numbers obtained for certification purposes must not require “exceptional piloting skill or alertness.” Standard runway performance assumptions include a “smooth, dry or wet, hard-surfaced runway,” perhaps one that is grooved or porous to enhance wet surface friction; standardized relative humidity values; a regulatory 2-sec. engine failure pilot recognition delay; and flawless anti-skid braking performance, among other idealized conditions.
What's not written into the regulations, though, can have a critical impact on actual aircraft performance on any given day in your flight operations schedule. The airplanes you operate may not be brand new. Runways may undulate, causing partial loss of weight on wheels or changes in pitching moment. Surfaces may be contaminated with dust, light debris, tire residue and oil droplets, along with pools of standing water, ice, sleet or snow. Gusting winds may make precise speed and directional control considerably more challenging compared to idealized certification flight test conditions. One or more of your tires may blow, your engines may eat birds at rotation, your nose wheel steering could malfunction.
“You're being naïve if you believe you'll always operate in ideal conditions. Real world conditions show us how sterile is the certification flight environment. You have to respect the world in which you're operating. So, don't bet your life on book numbers,” says one experienced flight department manager with a fleet of 17 aircraft.
Even under highly controlled flight test certification conditions, most average line pilots cannot achieve the same results as test pilots because of the shock and awe of an unexpected emergency.
“There is fog, there is chaos in the real world when an emergency occurs. We can't just flip into an ideal test pilot mindset,” the flight department manager said. This even can occur during the controlled conditions of certification flight test. Experimental test pilots for several business aircraft manufacturers have suffered fatal accidents during certification work. “There are unforeseen things that can just reach up and smite you.”
Surprises are few and far between for test pilots. They have the luxury of knowing that the emergency condition will happen in advance. That enables them to carefully rehearse each test point written on a flight test card, so as to extract ideal performance from an aircraft. So prepared, they can fly the emergency condition profile with great precision and near perfect timing. If the test doesn't go as perfectly as planned, they can repeat the procedure until they extract the performance they want from the airplane. It's a little like the “do-overs” pilots practice in flight simulators.