Dry but not high

Photo: © CASA

by Terry Clark

This 60-year-old, male, low-hour pilot with about 100 GA hours and 50 RA hours was the proud new owner of a neat pre-loved SK220 Jabiru. My plan was to fly to NATFLY at Temora from my home base in SE Queensland. In preparation I conducted six cross-country sorties ranging in duration from one to four hours.

On the sixth flight I planned a route from base to Maryborough, Tin Can Bay and home: a total of 235nm with an estimated flight time of 2.9 hours. I calculated fuel onsumption at 15 litres per hour, giving 43 litres plus a 10 per cent (or 4 litre) variable reserve and 30 minutes (or 8 litre) fixed reserve, making a total of 55 litres. Before leaving, I noted the fuel tank visual level was at least 55 litres from a maximum 63 litres.

Until the final stage, the flight was uneventful, with a brief stop in Maryborough. There I checked the fuel and engine time elapsed, noting that 37 litres remained after 1.5 hours, which was 0.2 hours longer than estimated, but the fuel consumption was still within planned parameters. On the 30nm leg to Tin Can Bay headwinds were higher than forecast, but I didn’t change the cruise power setting of 2850 rpm and accepted a groundspeed penalty which added 12 minutes. En route from Tin Can Bay to home I made a small diversion to avoid some rain. That added about six minutes.

About 20 minutes from home I asked my passenger to visually check the fuel tank behind the seats. She said she couldn’t clearly make out the level, but thought fuel was visible. I was happy with this until a few minutes later, when the engine suffered unmistakable fuel exhaustion. Switching on the booster pump and reducing power to 2000 rpm gave about another two minutes of power and time to find a suitable landing spot.

The engine cut out at 2200 feet AGL and fortunately a lovely smooth cow paddock was within easy gliding range. I made a three-leg circuit and landed with full flap into the wind, with a 200-metre ground roll and no damage.

I broadcast Mayday on the area frequency, but some of the transmission was lost as we neared the ground out of VHF line-of-sight. On the ground there were no radio comms, so I called 000 on my mobile and asked the police to contact Brisbane Centre to let them know we were down safely.

Within a few minutes the police, AMSA and the RAA ops manager had all called to check that things were OK. Their response and concern were impressive.

Next I ambled over to a nearby house to greet the farmer, who hadn’t seen my silent arrival. He was mildly surprised to see the elegant addition to his cow paddock and commented that many planes conducted simulated engine failures over his farm, but I was the first to actually drop in for a visit. He obliged with a jerry can of fuel and helpfully pointed out some power lines at the bottom of the paddock.

My passenger and I walked the intended take-off path, clearing away a few rocks and sticks. I then explained to the farmer that I would do a short field take-off to avoid bumps and the power lines. But when I applied full power and released the brakes the Jab didn’t move … its left-hand tyre was firmly stuck in a big, wet cowpat! The farmer helped us get unstuck; we took off, and arrived home only an hour later than planned.

I undertook a detailed analysis of what had happened and after checking for any obvious fuel leaks and finding none, the next thing I noticed was total engine time of 3.5 hours compared to my planned 2.9 hours: a difference of 36 minutes, or nine litres at 15 litres per hour. The headwind and diversion accounted for a maximum of 18 minutes, an unexpectedly long backtrack at Maryborough about six minutes, and run-ups and pre-take off checks another six minutes. The remaining 18 minutes were the extra take-off and leg home after refueling.

Next I considered fuel consumption. All 55 litres were consumed in 3.3 hours, giving an average of 17 litres per hour. Both the technical manual and previous owner assured me that 15 litres per hour using 95 UL MOGAS on a cruise setting of 2850 rpm was reliable for cross-country planning. This figure had proved to be accurate on my six previous sorties.

There are two significant things to note in relation to fuel and this particular aircraft:

1. There is no electric fuel gauge or flow meter. The translucent fibreglass tank is graduated visually in 10-litre increments. The 95 UL MOGAS is straw-coloured and less easy to judge once the level falls below about 15 litres. The 98 UL MOGAS (red) and 100 LL AVGAS (green) both provide more contrast and make judgment easier and more accurate at lower levels.

2. While 95 UL MOGAS is an approved fuel for the SK2200 Jabiru, consumption will be lower using 98 UL MOGAS or AVGAS.

Lessons learned:

1. My time calculations were wrong. My planned groundspeed of 90 knots was too high and I didn’t allow enough time for run-ups, taxiing, headwinds and diversions.

2. I relied on an overly optimistic fuel burn estimate. The aircraft’s technical manual and previous owner’s experience should only be used as a guide, because an engine with 450 hours TTIS may not return the same fuel burn as a newer one.

3. Fixed and variable reserves are fine as concepts, but not much use if your planning is flawed from the outset.

4. I should change to 98 UL MOGAS or AVGAS as these not only give better fuel economy, but also allow a more accurate visual reading of the level in this plane’s tank.

5. I was slack. Completely filling the tank (only an extra eight litres) would have got us home with 20 minutes to spare.

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