Invicta International Airlines Flight 435 (IM435) was a Vickers Vanguard 952, flying from Bristol Lulsgate to Basel-Mulhouse, which crashed into a forested hillside near Hochwald, Switzerland on 10 April 1973. The aircraft somersaulted and broke up, killing 108 people, with 37 survivors. To date, this is the deadliest accident involving a Vickers Vanguard and the deadliest aviation accident to occur on Swiss soil. Many of the 139 passengers on the charter flight were women, members of the Axbridge Ladies Guild, from the Somerset towns and villages of Axbridge, Cheddar, Winscombe and Congresbury. The accident left 55 children motherless and became known in the British media as the Basle air crash.
Pilot Anthony Dorman became disoriented, misidentifying two radio beacons and missing another. When co-pilot Ivor Terry took over, his final approach was based on the wrong beacon and the aircraft crashed into the hillside. Dorman had previously been suspended from the Royal Canadian Air Force for lack of ability, and had failed his United Kingdom instrument flight rating test eight times. As a result of the crash tougher regulations were introduced in the UK.
Despite the conclusions of the official Swiss report, one commentator, ex-KLM pilot Jan Bartelski, has argued that the pilots may not have been entirely to blame and that there is a possibility that they were led off course by "ghost" beacon transmissions caused by electric power lines.
Flight
The aircraft was a Vickers Vanguard 952, registered as G-AXOP, and was chartered by a tour company based in Britain. Flight 435 took off from Bristol (Lulsgate) Airport, Lulsgate Bottom, North Somerset, United Kingdom for EuroAirport Basel Mulhouse Freiburg International Airport in Basel, Saint-Louis, France. The airport was located just miles from the border of Switzerland and Germany. Early on the day of the crash flight, the aircraft departed from London's Luton International Airport and made a short positioning flight to Bristol where 139 passengers boarded.
At 07:19 UTC, Flight 435 took off from Bristol. Captain Anthony Dorman flew the plane, while his co-pilot Captain Ivor Terry was handling communication. The flight was uneventful until its first approach. It was daylight at the time, so visual references could be easily obtained by the crew. However, a heavy snowstorm was reported in Basel, thus reducing the visibility there.
While approaching Basel, Flight 435 passed two approach beacons, named as beacon MN and BN, the latter of which was the outer marker of the Instrument Landing System at the airport. However, the aircraft overshot. Captain Dorman then initiated a go-around.
At 09:08 UTC, while Flight 435 was manoeuvring for its second approach, Basel Control Tower received a telephone call from a meteorologist and a former aircraft commander reporting that barely two minutes previously, Flight 435 had flown above the Binningen Observatory (approximately eight kilometers southeast of the airport) at a height of around fifty meters while heading south; he urged the crews of Flight 435 to climb immediately. During the approach, several passengers briefly saw several houses on the ground. While the meteorologist was still on the phone, the crew reported that they had passed the first beacon, named as MN. They were instructed to pass the second beacon, BN. In reality, when the crew reported over MN, they were actually in the vicinity of a third beacon, BS, and had already overflown the airport, heading south.
At 09:11 UTC, Zurich Area Control Centre asked Basel Control whether they had an aircraft which was flying outbound from the airport towards Hochwald, as they had observed an unidentified echo on their radar screen, a few miles south of Basel. Basel Control Tower denied this, but when the controller checked his radar screen he saw an unidentified echo moving to the south, a few miles from the airport. Notwithstanding this, Flight 435, having reported that it had passed beacon BN, was given a landing clearance.
After finishing his telephone call with Zurich, the Basel controller asked if Flight 435 was sure that they had passed beacon BN. Flight 435 replied that they had a "spurious indication" and that they were joining the localiser, an electronic signal marking the extended centre-line of the runway. The crew then confirmed that they were established on the glide path and localiser, while the controller stated that he could not see them on his radar screen. The controller then informed the crew: "I think you are not on the...you are on the south of the airfield." Flight 435 didn't respond. After this message, all calls to Flight 435 went unanswered.