Date of Accident: 10 August 2006
Time of Accident: 1540Z
Aircraft Registration: ZS-NUY
Type of Aircraft: Cessna T210M
Pilot Licence: Commercial
Licence Valid: Yes
Age: 31
Total Flying Hours: 2143.6
Hours on Type: 456.5
Last point of departure: Witbank Aerodrome (FAWI)
Next point of intended landing: Kitty Hawk Aerodrome (FAKT)
Location of the accident site: On an open field approximately 0.3 nm east of Kitty Hawk Aerodrome
Meteorological Information: The weather was fine; Temperature: 28°C; Wind: NNW/Calm
Number of people on board: 1+2
Number of people injured: 1
Number of people killed: 0
Synopsis
On the morning of 10 August 2006, the pilot departed from Wonderboom Aerodrome on a private flight to Ulundi Aerodrome in KwaZulu-Natal. En route, he landed at Kitty Hawk to pick up two passengers, one of whom was an employee of a vehicle tracking company. He then proceeded to Witbank Aerodrome, where he collected another two passengers. From Witbank, they headed for Ulundi Aerodrome, where they landed at about 0900Z after an uneventful flight.
At approximately 1230Z, the pilot, accompanied by the same passengers, departed from Ulundi Aerodrome on the return flight. He landed back at Witbank and dropped off two passengers, and then took off for Kitty Hawk to drop off the remaining two. After flying for about 15 minutes, he started the descent for Kitty Hawk with full flaps and at an indicated air speed (IAS) of 65 to 70 kts. Directly after he made a radio call on frequency 120.65 MHz, reporting right base for landing at Kitty Hawk, the engine suddenly lost power and subsequently failed.
He immediately switched the fuel selector to the opposite fuel tank and turned on the boost pumps to restore engine power, but to no avail. As the aircraft was losing height and unable to glide safely for landing on Runway 01 at Kitty Hawk because of power lines ahead, the pilot executed a forced landing on a grass field east of the runway. The aircraft landed with the undercarriage retracted, skidded for about 40 metres and ground-looped through 90° before coming to rest.
The aircraft sustained damage to the right wingtip, underside of the fuselage and propeller blades. The pilot and passenger seated in the front seats were unhurt, but the vehicle tracking company employee, who was seated in the left-hand rear seat, sustained injuries to her back, neck and pelvis.
Probable Cause
The fuel tank outlets became uncovered when the pilot manoeuvred the aircraft as the fuel tanks were less than 1/4 full. This caused fuel starvation and engine stoppage.
Jim’s Analysis
Cessna singles have slightly iffy fuel systems. No, there is nothing really wrong with them, but they do need a bit of understanding. This is particularly important when you want to know exactly where the fuel is, and how to get it to the engine.
This guy may have had more than an hour’s fuel in the tanks when the engine died of thirst, but either didn’t really understand the fuel system, or didn’t have his mind on fuel management.
Yes, I have been down this road before, but Cessna fuel accidents keep happening, so I will keep nagging about it. We will look at this accident first, and then think about some other aspects of fuel management, mainly for Cessnas.
The pilot made two life-threatening mistakes. Firstly, he seemed to believe the fuel gauges. Surely, we were all taught, on our very first flying lesson, that you should never believe aircraft fuel gauges. Secondly, he didn’t understand the simple principle that the fuel goes where the ball goes. If the ball is to the right, then all the fuel–in all the tanks–moves over to the right-hand side of the tanks. So, if the fuel is lowish, it can slosh away from a tank’s outlet pipe, and cause a condition known as unporting. This means that the outlet pipe is sucking air–no fuel is getting through to the engine–so it will stop, which is exactly what happened to this bloke.
This is so unnecessary – it didn’t have to happen. It endangered lives and put up all our insurance premiums.
The pilot should have been aware of possibility of unporting if he didn’t keep the ball in the middle when the tanks were low. Once he started manoeuvring for the landing his attention would have been largely outside the cockpit and not watching the ball. This is just as it should be – but not when the fuel is dangerously low.
Now we come to a part that I find difficult to understand. The report says that the pilot joined right-hand base for Runway 11, but it seems he must have been too high, otherwise why use full flaps at that stage?
Can a 2000-hour pilot really stuff up his descent this badly? Of course I don’t know what he was doing, but whatever it was, it makes a strong argument for keeping the threshold within gliding distance, especially when the tanks are low.
Anyone who has flown a C210 will know that if you put out the gear and full flap, the aircraft doesn’t so much descend as plummet. But this may not be what actually happened at all. The CAA have once again excelled themselves with a really crappy investigation here – so the "facts" may not be facts at all.
So, we have this experienced pilot thinking he is very high on base leg. Then he sees that he is not too high at all – in fact he is not going to get to the runway. He opens the throttle, but nothing happens, so he throws it in a field.
But wait a minute – the wheels were up when he landed. Why would that be? He was on right base for landing on 11, and he was too high. Surely he would have had the wheels down?
OK, now let’s look at the Cessna-specific fuel problems, which are largely caused by two things. The first is that the small dihedral means that the ball doesn’t have to be far out of the middle for the fuel to move laterally in the tanks. Second, Cessnas–for reasons that I don’t fully understand–are inclined to allow fuel to cross-feed both on the ground and in the air.
On the ground, this means that the aircraft must be absolutely level when you refuel, otherwise you are in danger of not properly filling the tanks. In fact, I have it seen it recommended that after filling both tanks, you then top up the first tank again because while you were filling the second, some fuel has already cross-fed from the first.
Then if you leave the aircraft parked on a lateral slope, fuel will cross-feed to the lower tank and overflow. So if you leave a full aircraft overnight on the grass, it could easily have dumped an hour’s fuel by the morning.
Cross-feeding in the air, due to the ball being slightly out of the middle, has two results. It can lead to fuel overflowing from one tank and going out of the vent, so you have no reliable way to manage your fuel by timing. If you get say three hours out of the left tank, you could get only an hour-and-a-half out of the right one.
Finally, on all high-wing aircraft, pilots are inclined to skip the all-important duty of visually checking the quantities through the filler cap. It’s just too damn difficult to get up there and do the job properly.
All these little problems can quickly combine to give you an engine stoppage when you think you have a comfortable hour to spare.
What Can We Learn
- Plan the descent well in advance.
- It is vitally important to understand your fuel system.
- When sideslipping, always select the upper tank. So, for a left sideslip use the right tank.
- The fuel goes where the ball goes – in the air and on the ground.
- Visually check the fuel no matter how inconvenient this is.
- Never trust an aircraft fuel gauge.
- With a small dihedral you are more likely to have sloshing and unporting problems.
- Don’t expect a Cessna single to give you the same amount of time out of each tank.
- If both tanks are low, it is better to run one tank dry at altitude, rather than have a nasty shock in the circuit.