I regularly fly my airplane some 250 pounds overgross. But, I do it legally, since its equipped with an STCd tip tank installation. The STC (supplemental type certificate) allows operation at a maximum gross takeoff weight of 3550 pounds, an increase of around 7.5 percent from the airplanes original 3300-pound gross weight when it left the factory.
But theres no paperwork accompanying the admittedly older STC providing performance charts at the higher gross weight. Theres no question performance suffers at the higher weight, but Im legally allowed to use the older, lighter weight in computing performance. To compensate, I make sure I use runways of adequate length when operating at the higher weight and higher-than-published airspeeds, accepting a lower climb rate. The tradeoff is worth it.
Whether by placing too much aboard, or putting it in the wrong place, loading an airplane outside its weight and balance envelope is relatively easy to do with most GA aircraft. Its one thing to know youre slightly over the gross weight and have the runway to handle it. Its quite another to overload the airplane and then fail to consider the impact on performance.
Background
On October 6, 2006, at 0945 Eastern time, a Cessna 177 Cardinal flown by its commercial-pilot owner collided with a power line during initial climb from the Berry Hill Airport (4A0) in Stockbridge, Ga. Visual conditions prevailed. The private pilot and two passengers were fatally injured; the fourth passenger died the following day. The airplane was destroyed by post-impact fire.
Before the takeoff attempt, a witness watched pre-flight preparations, asking the pilot if the aircraft was within its weight and balance limitations. The pilot expressed confidence it was, noting the airplane had “a little over tank of fuel.”
The witness watch the takeoff roll, noting the airplane did not get airborne until it was approximately 2000 feet down the 3000-foot-long runway. He recalled the engine was running at full power. The airplane barely cleared a tree at the departure end of the runway before stalling and impacting another tree. Shortly thereafter, an explosion was heard.
Investigation
The wreckage was located 509 feet from the departure end of the runway. Examination of the crash site revealed the airplane clipped trees and impacted a utility pole, becoming entangled in power lines. Crash debris extended 100 feet beyond the initial impact at the tree to the pole. There was no evidence of pre-impact mechanical malfunction involving either the engine or the airframe.
At the departure end of the runway are 38-foot tall trees located 190 feet from the displaced threshold. Additionally, there is a two-degree upgrade slope at the runways midpoint. This upgrade slope is not stated in the airport information.
In its investigation, the NTSB researched performance figures for the Cessna 177 Cardinal by reviewing the types Pilots Operating Handbook (POH). It found the published takeoff ground run to clear a 50-foot obstacle at sea level is 1575 feet. The POH states this is accomplished at a maximum gross takeoff weight of 2350 pounds and with 10 degrees of flaps.
Review of the accident airplanes weight and balance revealed it weighed approximately 2452 pounds at the time of the takeoff, or 102 pounds over gross. The NTSB did not calculate whether the airplane was loaded outside its CG envelope or initial rates of climb, either for the maximum gross weight condition or the accident airplanes actual loading.
Probable Cause
The NTSB determined the probable cause of this accident to include: “The pilots attempted takeoff over the allowable takeoff gross weight of the airplane and his failure to maintain airspeed during climb after takeoff.”
The NTSB finding offers no real surprise. Yes, the Cardinal was overgross, but only by 102 pounds, or 4.3 percent. According to the NTSBs POH calculations, the airplane should have easily taken off and climbed out at its gross weight, with almost half the runway to spare (more, if the 190-foot distance from the displaced threshold to the trees is considered. However, the NTSBs report doesnt include the meteorological information, such as wind velocity, temperature and altimeter setting, necessary to estimate takeoff performance.
Does being 4.3 percent overgross have that drastic an effect on takeoff performance? No. If it did, a lot more GA airplanes-perhaps mine included-would be running off the ends of runways every day.
The simple fact is any number of GA aircraft are flying a few percent overgross every day. Rarely is the actual loading of a personal airplane computed down to the last pound. When was the last time you personally weighed each passenger as he or she boarded your airplane?
Too, airplanes gain a few pounds in empty weight as time marches on. The result often is a GA airplane weighing at least 50-100 pounds heavier than its paperwork says, especially if-like most members of the fleet-its been a few years since the plane was accurately weighed.
Even if the accident pilot had consulted his POH, he probably would have found it didnt offer him the weight and runway condition options he needed. But, he may have accurately weighed everything, coming up with the answer he was 4.3 percent overgross. All things considered-and while were not advocating overgross operations-4.3 percent isnt much. Wed guess its somewhere down in the noise level when considering takeoff performance, perhaps akin to under-inflated main wheel tires.
Which leaves us with the question of why the airplane crashed. Performance should have been adequate, according to the NTSBs calculations. The probable cause statement includes a reference to the pilots failure to maintain an appropriate airspeed during the takeoff and initial climb. It should be fairly obvious that an overgross airplane should be flown at a higher airspeed to maintain adequate margin above stall. Further, rate of climb and other performance parameters will suffer at the higher weight.
Perhaps the accident pilot wasnt aware he was overgross and, therefore, failed to compensate. Still, the 4.3 percent overgross condition should have been easily dealt with, both by the pilot and the airplane. Which leaves us to wonder: Was there something else going on here, like an out-of-CG condition?
