Background
On 15 November 2017, a privately operated Cessna 182S, registration HB-CQZ, was involved in a serious incident during night taxi operations at Sion Airport (LSGS). The pilot, born in 1944, held a valid EASA Private Pilot Licence (PPL(A)) and had accumulated 1875 total flight hours, including 1448 hours on type. The aircraft was a single-engine, high-wing, four-seat monoplane with fixed tricycle landing gear.
Sequence of Events
The pilot conducted a night training flight under visual flight rules (VFR). After departing runway 25 at 17:35 LT, he performed several touch-and-goes. On the sixth and final circuit, he landed on runway 25 at 18:09 LT. The air traffic controller instructed him to vacate via Taxiway Golf. The pilot had never used Taxiway Golf at night before; he usually exited via Taxiway Foxtrot. After clearing the runway with the landing light on, he received clearance to proceed to the South-East apron. While taxiing on Taxiway Golf, the pilot noticed two bright red light sources on a hangar ahead. He then saw a passage bordered by blue edge lights to his left. Believing it to be Taxiway Sierra, he turned onto what was actually a road (Route des Aviateurs) that runs parallel to Taxiway Sierra. The road was approximately 5 m wide with a 1.5 m grass strip separating it from the apron. At the eastern end of the Grely area, the right wingtip struck a pole, damaging the strobe light. Shortly before Taxiway Foxtrot, at 18:13 LT, the aircraft's right wing leading edge hit a sign, bending it. The aircraft sustained minor damage. The pilot then used Taxiway Foxtrot to reach Taxiway Sierra and proceed to the South-East apron.
Pilot and Aircraft
The pilot was familiar with the airport from previous day and night operations. The aircraft's exterior lighting—navigation lights, landing/taxi light, red anticollision beacon, and two white strobes—were all functional. No mechanical defects were found.
Meteorological Conditions
Weather was dry at the time, with light wind, clear skies, and good visibility. Sunset occurred at 16:56 LT, with civil twilight ending at 17:29 LT and nautical twilight at 18:07 LT. The moon was below the horizon.
Airport Lighting
Taxiway Sierra, 18 m wide, lacked edge lighting along most of its length. In contrast, Taxiways Golf, Foxtrot, and the links to the Grely apron (Link 1, 2, 3) had bright, visible edge lights. Two high-intensity red digital clocks were mounted above the hangar entrance on the south side of the Grely apron. The road (Route des Aviateurs) had no mandatory instruction signs at its junctions with Taxiway Link 1.
Similar Occurrence
A similar serious incident occurred on 22 February 2017 at the same airport, when a DR400/180 (HB-KOW) mistakenly taxied onto Route des Aviateurs and struck two signs. The STSB published a summary report on 5 April 2017.
Investigation Findings
The investigation found no technical malfunctions that could have caused or contributed to the incident. The analysis noted that the lack of edge lights on most of Taxiway Sierra made it difficult to identify in darkness, while the bright lighting on other taxiways and the road may have contributed to confusion.