A bit of background of the ATC side :
Bedder believeit :
as a controller, I can't imagine, given the circumstances, to allow an aircraft to backtrack down a runway, with vis probably about 500 metres, and not, and I repeat not, be doubly sure that any aircraft lining up/awaiting take off, would not be fully appraised of the runway occupancy situation.
Remember this was 1977, not 2007 . Read one of the reports ( there are at least 4 , but the US APLA one is, and by far , the best one ) PM me if you want the link.
Taxi :
TFN was receiving without warning diversion of far more aircraft than it could park, that the main taxi way was used for parking, that taxi situation was not designed for 747s ( relatively new a few in 77 in the canaries ). Controllers had to devise their own ad-hoc procedures to taxi aircraft.
The reason was all that was a terrorist bomb on LPA and the situation in TFN was exceptional . ( probably a bit like Halifax on 9/11 If I may use this comparison )
Visibility : TFN, for those who know it, has this particularity to have Cu or St clouds “ sitting” on it with no warning.
15 minutes before the collision, Vis was 10Km with 1/8 clouds. At time collision it was 300m vis in light rain and fog, and 10 min after the collision you had 7km vis.
Visibility can change between the time you issue a clearance and the time it is executed.
Technical : runway center line lights were US ( Notam’ed) only 2 serviceable VHF frequencies and only a ground and APP controller ( due staff shortages no TWR controller was available ) No radar, no ground movement radar ( not a usual thing in 1977, especially not in a relatively small regional airport that TFN was )
The 2 controllers tried to do their best regarding the circumstances. Misunderstanding occurred ( not only on the KL side, remember the C3-C4 runway exit discussion on the PA CVR) and a lot has been learned and changed as a consequence .
Don’t be too harsh on to controllers, who knows what you would have done then under the same circumstances.