No obstacles and 4 running engines!
It was nearly catastrophic with an 80cm high a/f lighting fixture..... and all 4 engines pushing!
Despite the assertion that "commercial flights" can't or won't use strain guages to ascertain take-off mass, I believe that such a system should be mandated at the ealiest possible opportunity. All modern aircraft have the ability to determine temperature, altitude (but not weight),and an EGPWS database from which the FMS could calculate the required climb gradient.
This would not obviate the crew from having to calculate the take-off data themselves, but it would certainly prevent the kind of gross error that occurred at Melbourne/Jo'burg etc.