Smaller flight departments seldom have such capabilities, so some are inclined to use more conservative runway performance numbers. They also operate from non-Part 139 general aviation airports that don't have the same requirements for full-time staffing, aircraft rescue and firefighting, and airport security, plus fence maintenance, wildlife threat mitigation and signage and traffic control, along with pavement condition, lighting and airport facilities monitoring as airports approved for scheduled air carrier operations.
In short, operating out of a non-Part 139 airport may entail more potential risk from imperfect pavement, intrusions by wildlife, pedestrians or vehicles on runways, and uncharted obstacles.
There is a correlation between such risk factors and the diverse causes of aborted takeoffs in business aircraft. Agostino claims that only 8-10% of all aborted takeoffs in business aircraft are caused by engine malfunctions. Twenty-nine percent, in contrast, are caused by tire failures. There also are more frequent collisions with wildlife at non-Part 139 airports and more runway incursions.
But approved aircraft flight manuals only have accelerate-stop and accelerate-go takeoff performance numbers based upon accelerating to an engine failure speed and then either continuing the takeoff on the remaining engine(s) or aborting the takeoff roll and braking to a stop on the remaining runway.
“The data assume that you'll abort for any malfunction prior to V1 (loosely defined as the takeoff decision speed),” says Agostino. There is no AFM data for stopping an aircraft or continuing the takeoff after suffering a tire failure, among other hazards that might be encountered.
Agostino also said his pilots, while well trained and highly disciplined to follow SOPs, are subject to the same “shock and awe” reaction times as other line pilots. He claims most pilots cannot react to a takeoff emergency in less than 3.5 sec., resulting in an additional 1.5-sec. delay and adding as much as 200 ft., or more, to accelerate-go or accelerate-stop distances.
For all those reasons, Agostino's pilots add 10% to the published approved AFM takeoff field length distances. That assures they'll have extra runway margins to cope with emergencies, including engine failures, blown tires and other takeoff malfunctions. He also requires his pilots to use Part 135 factored landing distances, rather than basic Part 25 landing distances, for all the same reasons.
The flight department manager with the 17 aircraft fleet uses an even more conservative 15% margin for takeoff. If the approved AFM TOFL is 5,000 ft., for instance, he requires his pilots to use runways no shorter than 5,750 ft.
“We use the 'Chain of Pain' process. We'll allow pilots to use shorter runways, but such operations must be pre-approved by several managers in our flight department. If the request gets all the way up to my desk, the flight crews really will need mission critical justification. That hasn't yet been the case.”
Airline pilots long have had the advantage of practicing maneuvers at challenging airports in the simulator to achieve high proficiency. Airlines typically have data and terrain for most or all of the airports in their route structures programmed into their flight simulators because they fly to such destinations several times per week.