Tuesday, November 6, 2012
When To Abort
Aborting a flight—either on takeoff or in the sky— can be one of aviation’s most difficult decisions
The twin Cessna finally screeched to a stop, with two flat-spotted tires and burned-out brakes trailing smoke. I was able to turn off at the end onto the west ramp, but unable to taxi as the left engine was unresponsive and the brakes were pretty well fried.
The left throttle linkage had apparently snapped immediately after takeoff, probably a result of three years of corrosion in the salty, humid air of the Philippines. I don't usually deal in what ifs, but I couldn't help speculating what would have happened had the linkage waited another 10 seconds to break. By that time, I would have been out over the water. At 1,400 pounds over gross, the 421 would have stood no chance of flying on the remaining engine alone.
In this case, the abort was my only choice, but some instances may not seem so clear cut. Back in the 20th century, Cessna used to build a centerline thrust twin called the Skymaster. The design was intended to eliminate the minimum control speed (Vmc) associated with asymmetric thrust and improve the chances of surviving an engine failure.
There was one problem, however. The rear prop was a pusher mounted on the aft fuselage, out of sight and often out of mind. That meant some pilots would try to save a little fuel by taxiing on the front engine only.
Most pilots were smart enough to abort when full throttles didn't produce normal takeoff power, but incredible as it may seem, some Skymaster aviators would forget to start the aft engine—or to restart it if it had idled out—and initiate takeoff with only the front mill running.
It might seem impossible not to notice that the airplane wasn't accelerating properly, but several pilots still blundered off the end of runways wondering why their shiny Skymaster wasn't accelerating very well. Cessna solved the problem by placing the world's largest alternator-out light on the panel to indicate that one or both alternators weren't on line. Cessna also modified the takeoff checklist to require leading takeoff power with the rear (right) throttle first. If there was no response, fill in the blanks.
The more typical problem of determining when to abort a departure is usually a fairly simple decision. In a single, ANY anomaly that affects the airplane's ability to lift off and climb or distracts the pilot should be cause for retarding the power and aborting the takeoff, assuming there's adequate runway remaining. In addition to the obvious loss of partial engine power, that includes an electric fuel pump that's inop, a door or window that pops open, flaps that refuse to retract or extend properly, a seat that won't adjust, an oil-filler cap that's not properly tightened, the odor of electrical smoke in the cockpit.
This isn't to suggest that many of these problems can't be dealt with in flight. The difficulty is that takeoffs are perhaps the most demanding segment of flight and require your undivided attention. If you have the option of dealing with these difficulties on the ground, you'll be less liable to become distracted and perhaps fly the airplane into the ground.
Unfortunately, not all aborts are associated with takeoff, though problems during departure may be the most critical. Perhaps the more difficult decision is related to aborting a flight already in progress and performing a precautionary landing. This could be a result of extremely adverse weather, poor fuel planning or a number of other circumstances. If there's an airport nearby, the choice is simpler, as there's little chance of damaging the airplane.
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Labels: Decision Making, Features, Flying Skills, Learn To Fly, Pilot Guide, Pilot Skills, Safety, Pilot Safety