Margins to live by

Failure to climb

The CFI owner, a commercial pilot, and a student flew a Piper Cherokee 140 into Gastons Airport (3M0), a resort strip in Lakeview, Arkansas, in October 2002 for dinner. They needed to depart before dark because the 3,200-foot grass runway was unlit. Obstructions dictate one way in and the other way out. The weather was good VFR with light winds and a temperature of about 60 degrees Fahrenheit. Witnesses noted that the aircraft was slow to accelerate and used nearly all the runway. After takeoff, the aircraft was observed nose-high and not climbing.

The Cherokee hit a bluff 1.3 miles from the airport at an elevation of 709 feet, only 166 feet above the airport elevation. There were no survivors. Because of impact damage and fire, it was impossible to determine how well the engine was operating. The flaps were set at 25 degrees, the recommended short-field configuration.

The 67-year-old CFI had just more than 4,000 hours total time ,with 579 hours in make and model. The 1967 Cherokee airframe had about 5,400 hours, and the engine showed 1,778 hours since last overhaul. The annual inspection was current. Of interest, the CFI had mentioned to the home FBO that he was troubleshooting a “low power problem.” A sales receipt showed that the pilot had purchased six intake gaskets, although there was no logbook record of any maintenance of this sort. The pilot subsequently reported that the problem had been fixed.

Takeoff weight was not discussed in the NTSB accident report so it’s assumed not to be a factor. The exceptionally long takeoff roll begins to tell a story, but it’s impossible to determine specifically why the aircraft used so much runway and climbed so slowly. The NTSB determined the probable cause to be the “pilot’s failure to maintain clearance with terrain while maneuvering.”

Lance heavy

A Piper Lance operated by a flying club in St. Louis was flown to the same Arkansas resort airport for a fishing trip in June 2009. The PA–32R-300 departed the Spirit of St. Louis Airport, where the shortest paved runway is 5,000 feet, overweight by about 344 pounds.

As the Lance left the resort in the morning the weather was reported as “hot and muggy” with little wind and a temperature of 81 degrees F. With an airport elevation of 479 feet, density altitude was computed to be 2,367 feet. An employee observed that all six seats were filled, and the aircraft appeared overloaded since the passengers had luggage on their laps. Just prior to takeoff the pilot mentioned to the front-seat passenger that they were going to need the entire runway, but elected not to use flaps—although that is standard short- and soft-field procedure for the PA–32.

Taking off on 4,000 feet of pavement usually isn’t much of a challenge—but add turf, obstructions, and slope, and it becomes more complicated.The takeoff was videotaped and a portable GPS on board recorded the crash. The aircraft lifted off at the far end of the runway, dropped into a shallow valley, touched down a second time, hit a tree and rolled several times. A witness at the airport saw the airplane disappear into the valley, and when it reappeared it was “In a slight climb, the wings were wig-wagging, and it was porpoising.” The aircraft crashed a little more than one-half mile from the end of the 3,200-foot runway. There were three fatalities, including the pilot.

The 52-year-old pilot, a flying club member, had about 674 hours total time with 165 hours in the accident aircraft. He had completed a flight review in the accident aircraft three months prior to the accident.

The 1977 Lance had 9,011 hours total time and 2,108 since major engine overhaul. No aircraft anomalies were noted. A portable GPS showed the aircraft didn’t achieve flying speed. Maximum speed attained was about 68 knots and the maximum altitude was 508 feet msl, or about 29 feet agl. Despite not being refueled prior to takeoff, the Lance was estimated to still be 188 pounds over maximum gross takeoff weight. The CG was within limits but well aft.

According to the NTSB, the pilot’s operating handbook projected a flaps-up takeoff to clear the 50-foot obstacle at about 2,900 feet, with ground roll estimated at about 1,700 feet. That’s based on 3,600 pounds (maximum takeoff weight and below the actual takeoff weight) on a paved, level, dry runway, becoming airborne at 64 knots and accelerating to 69 KIAS at the obstacle.

With flaps set to 25 degrees, a maximum-performance takeoff profile on a paved, level, dry runway would yield a liftoff speed of 53 knots, a climb speed of 58 knots, a ground roll distance of about 1,210 feet, and an obstacle clearance distance of about 2,150 feet. Those were not the conditions encountered. To clear a 50-foot obstacle, using the club numbers and maximum-performance configuration, investigators estimated an obstacle clearance distance of 1,870 feet. That’s optimistic compared to factory numbers.

Perhaps more telling is the warning in the POH: “The performance charts are unfactored and do not make any allowance for varying degrees of pilot proficiency or mechanical deterioration of the aircraft. Effects of conditions not considered on the charts must be evaluated by the pilot, such as the effect of soft or grass runway surface on takeoff and landing performance. Warning: Performance information derived by extrapolation beyond the limits of the charts should not be used for flight planning purposes.”

The NTSB determined the probable cause to be “The pilot’s poor judgment/decision making in attempting the no-flap takeoff, his failure to comply with weight and balance limitations, and his failure to calculate the airplane’s performance under existing conditions.”

Too much elk

In late September 2005, a hunter and his friend planned to leave the Flying B Ranch near Salmon, Idaho, to return to California in a Cessna P210. They had bagged an elk and the hindquarters were estimated at 75 pounds each. They had front quarters as well. The pilot told the passenger they could put at least 160 pounds of weight in the rear compartment. According to the NTSB, “The passenger loaded the two hindquarters and then put in two sleeping bags, a shirt, a pair of pants, a felt hat, and some Styrofoam packing.”

The common theme is that when runways are shorter and rougher than what most pilots are used to, performance will be less than normal.A resort employee reported seeing two seats in the rear of the airplane’s passenger compartment. In front of these seats, the pilot and passenger loaded the two front quarters, two rifles, two duffel bags, two scabbards, a backpack (possibly two), a small saw, saddlebags, and the antlers. Additionally, this area contained “three shopping bags with merchandise they had just purchased in the store (three vests, two T-shirts, one jacket, and one visor)” and a container with aircraft window cleaning supplies. Each duffel bag was estimated at about 75 pounds.

The ranch’s privately owned turf strip was 2,000 feet long, running north and south, with a ridge across the approach end of the south runway. Field elevation was 3,647 feet.

The plan was to leave in the late afternoon and to refuel at Boise, Idaho, some 100 miles away. Even with relatively light fuel, the load was impressive. The density altitude was 4,793 feet, and the winds were calm. Two witnesses described the takeoff as taking nearly the full length of the runway and that the aircraft was “wallowing back and forth.” According to the NTSB, witnesses “watched the airplane as it veered left,...crossed the river and impacted the ground tail first, the nose slammed into the ground…and it came to rest inverted and caught fire.” There were no survivors.

This 1979 P210 had been modified with a turboprop engine about four months prior to the accident. The manual for the modified aircraft estimated takeoff from a dry grass runway to require about 1,580 feet of ground roll and a total distance to clear a 50-foot obstacle as 2,461 feet. According to the NTSB’s estimate, the aircraft was within weight and balance limits and the flaps were set to about 15 degrees as determined from the wreckage. The investigators could find no abnormalities with the engine or aircraft.

The private pilot had just less than 2,000 hours total time, with just more than half of that time in an unmodified P210. He had completed 15 hours of transition training after the aircraft was modified and had only flown an additional seven hours since. The NTSB attributed the accident to “the pilot’s failure to obtain airspeed during the initial takeoff climb, which resulted in a stall/mush and subsequent collision with terrain.”

Commentary

The common theme is that when runways are shorter and rougher than what most pilots are used to, performance will be less than normal. Sparky Imeson, who wrote many books on mountain flying, suggested that the aircraft should have at least 70 percent of liftoff speed at the runway halfway point—or reject the takeoff. The formula does not guarantee climb gradient to clear any obstacles or terrain.

Some more caveats: Reduce the load. Seriously. Whether it’s fuel, baggage, or elk parts, most general aviation aircraft perform poorly at maximum weight, especially at higher density altitudes. UPS or FedEx will pick up almost anywhere to take the excess baggage and elk. Most aircraft will land shorter than they’ll take off, so pilots can get wedged into a place that isn’t easy to leave. Wind, temperatures, and obstacles often amplify negative performance.

Finally, it’s likely that neither we nor our aircraft will mimic POH performance, because those conditions are carefully controlled and will not be the same—engineering reality, operational fiction. The AOPA Air Safety Institute recommends a 50-percent margin over whatever the book says. So if the book says 2,500 feet just to clear the 50-foot obstacle under ambient conditions, let’s make it 3,800 feet. Be sure the aircraft is configured properly, the engine is pulling well, and that you have practiced the short/soft field procedure in the actual aircraft. It’s a margin to live by.