Heavy airplane, density altitude bad combo

Aircraft: Cessna 206. Injuries: 1 Minor. Location: Arcadia, Fla. Aircraft damage: Substantial.

What reportedly happened: The density altitude at the time of the accident was calculated to be about 2,300 feet. The pilot, who was attempting a water takeoff, used 10° of flaps to get the airplane off the water. It climbed to about 400 feet but would not maintain altitude and began to descend. The pilot executed a forced landing into a field where the airplane collided with trees.

After recovery of the airplane, the engine was removed and test run. No pre-accident mechanical malfunctions or failures were found that would have precluded normal engine operation.

A review of the performance chart revealed that the airplane, in a clean configuration and at a maximum gross weight of 3,800 pounds, should have been able to maintain a rate of climb of 600 feet per minute. Although the pilot estimated the gross weight was 3,695 pounds, post-accident weight and balance calculations revealed the estimated weight of the airplane at takeoff was 3,855 pounds, which was 55 pounds above the maximum allowable gross weight.

Investigators determined that it is likely that the high density altitude combined with operation over the airplane’s maximum permitted takeoff gross weight resulted in the airplane’s inability to climb or maintain altitude.

Probable cause: The pilot’s decision to take off in high density altitude conditions with the airplane over its maximum gross weight, due to the pilot’s improper weight and balance calculations, which resulted in the airplane’s inability to climb or maintain altitude.

NTSB Identification: ERA11LA451

This August 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

Comments

  1. The weight is stated as “estimated” it may well have weighed more. The flaps were set at 10* and lowered a further 10* after take-off, the 600 fpm book climb rate is for a “clean configuration,no flaps. The actual weight may have been a little more than the 55 lbs.( the numbers were estimated by the pilot), the temperature/humidity may have been a little different the weather report was from 26 miles away. It was a water take-off, how much weight(water) was in the floats?,they were destroyed in the forced landing. It seems reasonable to me that the cause was to heavy,high density altitude and high drag from 20* of flaps that would not allow the 206 to accelerate.

  2. Perhaps the post-takeoff power reduction was a factor? This story does not compute.

  3. A 206 wouldn’t even know it was 55 lbs. over gross and at 2300′ density altitude. Sounds to me like he got too slow and didn’t lower his nose and ended up mushing in. I don’t think you could get the temperature hot enough in Florida to equal 12,300′ density altitude as Kevin suggests. I think the NTSB screwed up on this one.

  4. There’s something screwy about this accident report. A DA of 2, 300 feet will not prevent a 206 from climbing decently, and a 55-pound weight excess won’t either. Could the report have mis-stated the DA? Perhaps it was 12, 300 feet instead of 2, 300?

  5. I agree with Ken and John. There’s more here than was reported. Why did the airplane begin to descend? It didn’t get heavier. And if it was able to climb to 400 feet why couldn’t it continue to climb. 2,300 feet isn’t very high and 55 pounds isn’t very much–I doubt that either is the primary causal factor in this accident.

  6. If the book says the 206 can climb at 600 FPM and he climbed to 400 feet….yeah, I guess that extra 55 lbs just did it in. NTSB really said that?

    • Ken Deken says:

      Good point, seems to me there was more to this one than shown here. 2300 ft density altitude, 55 pounds over gross, a climb at 600 fpm and an initial climb well out of ground (rather water in this case) effect does not add up.

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