Fuel burnt out near Hay - passenger asked to watch:
Six of us spent a very pleasant weekend at the One Tree Picnic Races over a long weekend back in 1984. We landed on the Friday in a 206 at a property north west of Booligal. I mean miles from Booligal. On the Saturday, our host Graham Morphett drove us down to the One Tree Picnic Races. (between Booligal and Hay).
We left Canberra with well less than full fuel. We had some baggage with us so full fuel tanks were not a possibility. Graham could not supply us with fuel. We needed fuel for the return flight. On returning we flew down to Hay for fuel. On the way out to Graham’s the westerly wind proved to be stronger than forecast. We had enough fuel to make Hay and have some in reserve but not much.
On the flight from Graham’s to Hay, to be sure about the fuel situation, I decided to burn out the left tank. I was taught how to do this if concerned about fuel - never the right tank only the left. Circuits are usually to the left. In that situation if the fuel is low, it's the right tank fuel outlet which is covered in fuel. The left tank outlet may be exposed to air because the fuel falls to the left given the wing is tipping to the left in the circuit turns. Yes, a balanced turn is the aim – but they are never perfect. Fuel will fall away from the left tank outlet during a left turn.
If one moves the ailerons to rock the plane left and right, the fuel level indicator will usually move if there remains any fuel in a tank. On our way down from Graham's station, after the take-off I switched tanks from the right to the left. I rocked the plane, there was movement in the needle. However, soon the left needle became stationary - fixed on empty. There remains fuel in the line from the tank to the engine, but not for an extensive time. The trick is to determine as nearly as possible when the needle doesn’t move on a wing rock – you are then for all practical purposes running on the fuel line contents. In my experience the time before cut out varies from 12 to 20 minutes (in a 206) before silence prevails. This will depend on what power you are running and the mixture setting.
The weather that morning was not flash. A solid layer of cloud at around 2,000 feet above the ground, extended for as far as the eye could see. I stayed below it. This cloud proximity to land meant there was not the usual grace time to get the motor started in the event the fuel flow drops (in a fuel injected motor like this one) and the fuel tank switch is not caught in time. On a well- executed tank burn out, no one, save the pilot and perhaps the front passenger, is aware this has occurred. By closely following the fuel flow rate, one can switch tanks at the very first sign of a fuel flow drop - thus ensuring the engine remains with fuel without a hint of an issue.
To assist me, I asked Henry Packham the front passenger to not take his eyes off the fuel flow indicator and to shout “FUEL” when there was any drop in the fuel flow. I put him to the task when there was no longer any fuel needle movement. It had been a reasonably social night - the others were snoozing/sleeping. I was involving myself in some navigation given that this flight was before the simplicity of following a straight line on a GPS. Also, the plane had no auto pilot - I had to hands on to keep her straight and level.
Then it happened – Silence! Gone was the comforting sound of a constant engine noise. The plane seemed to jump around - those snoozing were suddenly 100% awake! As too was my front passenger. He was no doubt doing his best. I heard a faint “Fuel”. Shock had taken his voice.
I quickly changed the fuel to the right. We were going down. The prop was windmilling in the air flow - the mechanical fuel pump was trying to put fuel up to the injectors. I never turn on the auxiliary fuel pump in this situation. Perhaps that is a mistake. Also, I never turn the auxiliary pump on when changing fuel tanks.
A murmur, a splatter, a slight cough, then the steadily increasing sound of engine. We were back in business. The first time it’s a shocking experience seeing the manifold pressure shoot up as the engine goes quiet. I was not surprised but kept my eyes on the manifold pressure and more importantly, the fuel flow - waiting for the manifold pressure to come down and the fuel flow to show fuel – any fuel.
I suspect we only lost a couple of hundred feet but time does rush by. I was told to not touch the engine settings leaving the mixture and throttle as they were – all was good before so why change it? I suspect the fact the Cessna is a high winged plane and gravity keeps the fuel up to the fuel pump, makes a difference (some might say another of the many good reasons to only fly a single engine plane if the wings are on top of the plane). The Cessna 206 has a two-speed axillary electric standby fuel pump. I have never had to use it in a tank burn out, relying on the windmilling engine to pump the fuel.
The rest of the flight was uneventful if with attentive passengers.
© C.McKeown 2021.