We had been filming for several days up the Jungfraujoch in advance of the Jaguar car launch and had flown to Interlaken via Basel from Fowlmere in a Seneca III.
Interlaken is between Lake Thun and Lake Brienz in Switzerland and has steeply rising terrain requiring careful attention.
We had to position to Bern to clear customs for the return flight to Fowlmere and it was here that the left engine became flooded during a hot start. We managed to eventually start the engine after several periods of waiting for the starter to cool down.
The departure and subsequent flight towards Cambrai was IFR in IMC but relatively smooth. As we passed Cambrai the weather radar displayed heavy precipitation across our track and we soon encountered moderate turbulence and light icing.
It was dusk and we turned on the instrument panel lighting. Soon after doing this we had a complete electrical loss! Everything turned off but after a few seconds came back on again. This happened three times between Cambrai and Dover. Each time the auto-pilot disconnected and the HSI stopped slaving and of course all the avionics went ‘dark’.
We reduced the electrical load to minimum and watched the ammeter. I reached for the handheld VHF and tuned it to the frequency we were using and found my torch.
At Dover, London cleared us to leave controlled airspace by descent and passing 3500QNH we became ‘visual’ and 40mins later we were on final at Fowlmere with the battery operated runway lights guiding us in.
Subsequent investigation revealed the battery earth terminal had been reduced in size due to arcing, presumably due to our excessive starter cranking at Bern and was just making contact with the battery cable clamp! It is remarkable that we simply did not lose the electrical connection completely in the turbulence of the flight.
Reviewing ‘Electrical failure’ in a twin engine aircraft, the handbook refers to reducing the electrical load and how the remaining alternator can provide 65amps… In our case the loss of the earth terminal connection left nothing and it is sobering to reflect that in IMC you would be left with a compass and pressure driven instruments. Something worth bearing in mind!