 On 23 December 1972 at 16 : 30 , the company 's most fatal accident occurred . F @-@ 28 LN @-@ <unk> <unk> <unk> on Flight 239 from Ålesund to Oslo crashed at <unk> , killing 40 of the 45 people on board , including the crew of three . The cause of the accident was never discovered , although a possibility could have been faults with the instrument landing system . 
