Making the switch

So what was the cause of the engine power loss?

The investigation into the forced landing of Piper PA28-161, VH-SWV, on April 20 2017 at Camden airport, NSW, poses more questions than answers.

The ATSB investigation was released on February 12 2018. Investigation number AO-2107-046 refers.

The ATSB report rightly comments that all pilots should be prepared for the unlikely event of an engine power loss on take-off by knowing the correct glide speed and thinking ahead to put the aircraft down in the least obstructed area.

It is worth while reviewing the ATSB report to see if there may be something of interest for other pilots to learn for their safe flying.

The report states that the pilot started the engine and taxied the machine to the run-up bay. That took all of one minute. The left tank had been selected. It had some 50 litres while the right tank had 70 litres. In summary the fuel level was just below and above the inbuilt tank tabs. At the run-up bay normal pre-flight checks were carried out and then the right tank was selected. The fuel boost pump had already been turned on.

ATC cleared the aircraft for take-off and the pilot taxied forward and turned right onto the runway and throttled up for the take-off. It was after lift-off that the engine lost power.

Could the tank change be the clue as to the cause of the power loss? The problem is to prove it.

The right tank held some 70 litres of fuel but was less than full. The pilot had selected the right tank just before he got the take-off clearance and then moved forward to take-off. It is not unknown for aircraft to have fuel flow issues when a new tank is selected immediately before take-off followed by the demand for maximum fuel flow. A typical aircraft POH calls for use of the fuel pump when changing tanks for that very reason. Had the pilot selected the left hand tank with 50 litres a sharp turn to the right for the take-off might have allowed air to enter the fuel line.

Could it have been that air got into the fuel line leading to the engine? Probably unlikely given that the turn to the right would have pushed fuel towards the engine fuel line. Was there any splashing of the fuel in the tank immediately before take-off that may have allowed air to get into the fuel line? Was the fuel tank selector fully in the correct position? Could it have been that there was already air in the right pipe line and when selected a small amount of fuel was available to keep the engine running at idle or taxi rpm but not enough for the engine to establish and maintain the fuel flow required for take-off. That is the sixty four dollar question.

‘Could the tank change be a clue as to the cause of the power loss?’

The aircraft had been flown the previous day without any issues. The engine was a new installation and had done some 6.7 hours before the accident.

Could that also be a clue to the cause? History would say be wary of an aircraft in the 10 hours or so following maintenance work.

One thing that comes out of this event is that when selecting a new fuel tank, usually the fullest tank, it is best to do this and allow some 3-4 minutes between the change and the take-off power demand. If there is a fuel flow issue this should become apparent between the change and the take-off.

That time span could well be the taxi to the take-off point or just holding while waiting to take-off.

Now a little bit of history. Back in the 1960s and 1970s light twins were becoming the norm for a lot of new twin rated pilots. A few were caught out when, with less than full fuel, they did what is known as a turning type take-off. The fuel in the tank on the outside of the turn sloshed away from the fuel line and allowed air to get into it. That air got into the engine with a resultant power loss just as the aircraft got airborne or crossed the upwind fence. A critical time at low speed. There were a number of accidents, including fatals, as a result of this. In due course aircraft flight manuals and even cockpits carried statements saying ‘No turning type take-offs allowed’

It is unfortunate to record that the lessons of yesteryear get lost with the passage of time.

The safety message here is that for all aircraft, single or twins allow some time on the take-off fuel tank or tanks before the actual take-off. Do use the run-up tank for take-off. That will ensure a satisfactory fuel flow and secondly make slow turns onto the take-off runway and even hold for a few seconds to ensure an uninterrupted fuel flow. This is particularly so with less than full fuel. Do use the entire runway available. Aero engines run better on fuel than air.