The Problem with Lime

by Mike Feeney

New Zealander Ken Simpson was very wellknown, as he had been aerial topdressing since September of 1952 and had many hours of lowlevel ag-flying experience. Ken was one of the very early New Zealand top dressing pilot pioneers. Ken was the 14th ag-pilot to be killed in New Zealand and the first to lose his life in a Fletcher FU-24.

Although manufactured in the U.S., none of the FU-24 aircraft were certified there, at least not for many years later. Instead, they were flight-tested by a New Zealand pilot and issued New Zealand airworthiness certificates. In the minds of some of us, including myself who flew the early versions, the test-flying procedure seemed to be deficient in some respects.

On October 16, 1956, Ken and his loaderdriver began working on a lime job shortly after lunchtime. The airstrip was about four nautical miles east of the small village of Mananui and a few miles south of Taumarunui. The terrain in the spreading area consists of fairly steep hill-faces and patches of native bush with some rather solid trees. The wind conditions in the early part of the morning is often calm with patches of fog, but by midday there is always some wind that is often variable amongst the hill country.

Ken took off in his FU-24 on the day’s ninth sortie and at 13:40 crashed the aircraft. The accident investigator calculated the take-off payload must have been about 14 cwt (712 kg).

Before the crash, the aircraft was seen to be approaching the sowing area at low-level. Lime was seen to be leaving the hopper outlet for a few seconds and then the flow stopped. The aircraft was seen to be maneuvering at low-level within a narrow gully. It was then seen to enter a turn during which it struck a tree and crashed inverted in a group of trees. The impact was taken by the cabin area and Ken was killed instantly. Fire erupted and the aircraft was destroyed.

The investigator said that he found evidence of compacted lime present from previous flights and there was no doubt that a serious overload had happened. There was no evidence of an engine or structural failure. He also commented that a change in wind conditions was likely, leading to a loss of performance with no safety margin remaining.

With the hopper size of the early model FU-24, when 750 kg of super phosphate fertilizer was loaded, the hopper was full and could be observed by the loader driver as he filled the aircraft. But, lime is denser than super and the level of 750 kg would be well below full.

The aerial spreading of any product legally requires that 80% of the weight/mass must be able to be jettisoned within five seconds. After the advent of (dry) granulated superphosphate this was no longer a problem. But a product made by grinding limestone has proved to be a dangerous situation due to very poor flow factors with hoppers that are not fitted with some form of agitator in order to maintain a reliable rate of flow.

The FU-24’s hopper design was a concave shape from top to the bottom outlet. Lime products tend to form a bridge over the hopper outlet. When this happened, the only effective way to take the weight off the compacted material was to push the nose down (partial bunting) to remove the “G” loading to zero, or less, then pull the stick back to avoid hitting the ground, trees or wires. When flying at low-level, the process is very uncomfortable and rather dangerous in several ways.

Mounted behind the pilot’s seat, the front of the hopper had a small clear window. The pilot had to turn his head around to face backwards in order to try and read the level of the product. It was very difficult to see clearly through the window to check the load. In my experience, the window was far too small and became dirty usually after the first load. The only sure method of checking the payload was for the pilot before takeoff to undo his harness and climb onto the wing in order to look down into the hopper. It was also difficult for the loader driver to check unless he climbed out of his truck cab onto the ground, then climb up onto the wing and advised the pilot.

File photo of a Fletcher FU-24, this one powered by a 400 BHP Lycoming IO-720. The pilot, Murray Algie, stands on wing talking to a New Zealandfarmer. of performance with no safety margin remaining.

The Fletcher FU-24 cockpit ergonomics were also quite awful. I soon discovered this when I flew them after having become used to the fine Cessna C-180 in its ag configuration. For some strange reason, the pilot’s seat was mounted in the centre of the quite wide cockpit. This meant that you had to look over the nose-cowl from the middle. This left no space on the right or left side to carry your loader-driver or a farmer.

The hopper dump lever was placed well over to the left. Your arm angle was awkward and it was very difficult to operate the lever day after day with your left arm. When hauling lumpy chunks of damp lime, it was a nightmare trying to force the congealed mess through the manual hopper doors at the same time having to “bunt” the aircraft nose down at low airspeeds and with almost nil climb performance. The entire job could become utterly ludicrous and highly dangerous. Fatigue gradually wore one out and many of us grew to dislike the horrible machine.

The whole job of dealing with compacted lime was very dangerous without some form of agitator or aircraft weighing system. However in those early years, 99% of us persisted in trying to safely spread lime from hoppers which were not fitted with proper agitators. Why the New Zealand Civil Aviation officers, or company management, did not take very strong steps to ban the use of lime, or fit agitators, is a mystery to me; even after all these years and avoidable deaths, cockpit fires and injuries.

I experienced many battles with clogged lime in hoppers and survived by never flying into rising terrain. Instead, I used a higher airspeed and a sowing direction across the lie of the land. I also always landed with the hopper doors open, in the hope that shock and vibration might clear the inside of the hopper, which it often did not.

If only back in 1955 and 1956, some official with some brains and guts had grounded the fleet of FU-24s and called a working meeting and said, “OK chaps. Let’s not leave this room until we decide on how we are going to convert this heap of junk into a decent ag-flying machine we can be proud to fly.”

Mike Feeney of Hamilton, New Zealand is a retired professional ag-pilot and a long-time aviation journalist, technical and air safety writer. mikefeeney@actrix.co.nz