Incident Overview
On 11 May 1999, a Cessna 525, registration G-RSCJ, was en route from Palma, Majorca to Luton. As the aircraft approached the reporting point BARLU over the Cherbourg Peninsular, approximately 76 nautical miles south of Southampton, the right-hand fuel bypass light illuminated. The pilot initially advised ATC of a potential fuel contamination issue and declared an emergency, intending to divert to Southampton. Shortly thereafter, the pilot changed the diversion destination to Bournemouth. The aircraft was vectored for a left base to Runway 26 at Bournemouth and made an ILS approach. The pilot became visual with the runway at 3 nautical miles from touchdown and landed safely at 0842 UTC.
Post-Landing Inspection
After landing, an engineer removed both engine fuel filters and drained fuel from the left and right fuel systems. The fuel filters appeared clean, but the fuel in the filter housings was cloudy with what resembled 'an icy slush'. Fuel was drained until the cloudiness cleared, and the fuel filter bypass warning system was found serviceable. Two new fuel filters were installed, and the aircraft was refuelled with fuel containing an anti-icing additive. Subsequent analysis of the removed filters confirmed they were very clean, consistent with the aircraft's low operating time of 67 hours since manufacture.
Fuel Contamination Findings
The pilot later learned from the handling agents at Palma that the uplifted fuel did not contain any anti-icing additive. The aircraft flight manual limitations section specifies that all approved fuels must have anti-icing additive added if not already present. A caution in the manual reiterates the requirement for anti-ice additive (MIL-I-27686E) for most fuels and directs pilots to section III for blending and concentration checks.