AIRPORT operator BAA is investigating two near misses at Heath row's T5 last month.
It is believed two tower cranes collided and hours later a 13-tonne precast concrete column was dropped 9 m from another crane.
A BAA spokeswoman said: 'Two tower cranes were involved in a minor incident last month when the jib of one touched the ropes of another.
'In a separate incident, a crane driver took the precautionary action of lowering a precast concrete column out of the vicinity of nearby workers after he suspected a crane fault.
A lighting rig was damaged.'