In the Thai Airways A310 accident, the aircraft had a flap problem which was quickly rectified, however because the Kathmandu approach is so steep due to the mountains aircraft have to be in full landing configuration 13 nm before touchdown (ie full flaps, gear down) The aircraft was too high and abandoned the approach, but they failed to follow the correct procedure. There was confusion over what route the aircraft would follow to re-commence the approach, and entering that route into the FMS. ATC were not properly responding to the crews requests, which lead to more confusion. While the crew were distracted the failed to realise the aircraft had turned towards the north during the confusion and was heading towards mountains rising to 23000ft, the aircraft struck the mountains in level flight at 11500ft.
The PIA accident occured simply because the crew descended too low on the approach, ATC notified them they were too low seconds before the crash, but too late.
The main cause of both accidents was pilot error. The complex approach procedure at Kathmandu were contributory factors to both. Poor ATC also contributed to the Thai crash
Air Disaster: Volume 3