It is too early to speculate, but from the press releases I am reading, it seems the Singapore Airlines 747-400 may have collided with the wheel of another plane or some heavy excavation equipment. Just 2 months ago, fallen debris resulted in the loss of the Concorde.
I was watching this show called Airport on BBC America, and on one episode they showed ground check vehicles that work in between planes landing and taking off, to scan the runway for fallen debris and to clear it. I didn't realize the importance of their actions until now.
I think planes are very safe, it is the fact that there are so many operating, that ground density makes for compromised safety.
I want to ask everybody questions such as the following...
Who should be repsonsibe for such debris, the airline whose plane dropped it? or the airport? or is nobody to blame?
If anybody who reads this actually does manage runway maintainance, can you please give us some insight into your work?