Not a member? Join today. Already a member? Please login for an enhanced experience. Login Now
Menu

Off the charts: Don’t become an unintentional test pilotOff the charts: Don’t become an unintentional test pilot

WPR10FA287WPR10FA287

Air Safety InstituteBy David Jack Kenny

Few things in aviation are linear. Being 10 percent fast over the threshold can increase landing distance by 40 percent or more. Cutting power output in half doesn’t leave most aircraft cruising straight and level at half the speed. Those nonlinearities show up in the “Performance” section of any pilot’s operating handbook. Tables show progressively wider steps between entries as weight, temperature, and elevation increase; on charts, the lines representing those relationships are curved, not straight. A pilot’s guess at the shape those curves take beyond the range that’s actually shown will only be a guess—not the optimal level of precision for critical safety calculations.

A Piper PA32R-300 Lance departed Runway 11 of the Springerville Municipal Airport in Arizona a little before 2 p.m. on June 11, 2010. Less than two minutes later, it crashed into a high school in the neighboring town of Eagar. The post-crash fire consumed almost the entire airplane and caused extensive damage to the school; all four on board were killed. It took firefighters the better part of twelve hours to extinguish the blaze in the school. They weren’t helped by the boxes of ammunition on board the airplane that discharged during the fire.

A witness who watched the takeoff from a taxiway said that the Lance’s takeoff roll “used more runway than used by most of the other small aircraft during takeoff.” After takeoff, he saw it “rocking side to side,” climbing and descending three or four times with little net gain in altitude. Other witnesses saw it flying over town at a very low altitude—one estimated it at no more than 30 feet —and agreed that the engine noise was smooth and steady. Just before hitting the school, it began banking to the left.

Examination of the wreckage found no evidence of malfunction in either the powerplant or airframe before impact, but the fire consumed so much of the airplane that some crucial questions remain unanswered: the position of the throttle, prop, and mixture controls, for example, could not be determined. Likewise, the exact weight of the airplane before the crash is unknown, but based on the luggage recovered and the 76 gallons of fuel loaded just before takeoff, it was estimated to be about 3,400 pounds, 200 below maximum gross, with the center of gravity within limits.

Engine configuration is of interest because the elevation of the Springerville airport is 7,055 feet msl, and the temperature at the time of the accident was 77 degrees Fahrenheit. At the time of the accident, the AWOS reported a density altitude of 9,700 feet. Winds were gusty and variable, from directions swinging between 170 and 210 degrees at 24 to 32 knots. It has two runways, oriented 11/29 and 3/21. Runway 3/21 is longer, at 8,422 feet, and would have offered better alignment with the wind, but was closed for resurfacing at the time. Runway 11 is 4,603 feet, relatively short for high-altitude operations. The Lance took off in a crosswind component estimated to be between 21 and 32 knots and something between a five-knot tailwind and16-knot headwind component.

While the longer runway would have been a more attractive choice, there is no guarantee it would have been long enough. The investigators obtained the POH for the 1977 model Lance. The uppermost line of the takeoff performance charts shows a pressure altitude of 7,000 feet. Depending on the chart (flaps up or down, ground roll vs. obstacle clearance), the curve goes off the top of the page at temperatures between 38 and 48 degrees Fahrenheit. Takeoff requirements for that day’s conditions were literally off the charts—way off.

The Air Safety Institute recommends adding a safety margin of at least 50 percent to calculated takeoff and landing distances, but that depends on being able to calculate them in the first place. The information available to this pilot provided no assurance that the Lance could take off at all. The pilot was based in Florida, and whether he had flown at that field before was not reported, but in retrospect it seems pretty clear that he hadn’t done it under those conditions. The obstacle clearance distance needed by a 1977 Lance at 9,700 feet density altitude is a problem best solved by a professional test pilot with all the support that implies.

The classic remedies for density altitude include lightening the aircraft and waiting for cooler weather and more favorable winds (and, in this case, the longer runway). All of those seem to have been available. The reported purpose of the flight was sightseeing over the Grand Canyon, which probably could have waited for another day.

And there’s a case to be made for limiting hazardous cargo to that which is needed on the trip. The boxes of ammunition likely weren’t necessary for the sightseeing trip. Had the crash otherwise been survivable, the discharge of ammunition during the fire could have prevented rescue.