I got this info from
a thread on airliners.net started by the movie maker, KDTWflyer.
Originally Posted by KDTWflyer, the maker of the movie.
- "The gear retraction sequence appeared to me to be within a normal timeframe following Vr." (A picture of this flight on climb out)
- 'There was a DTW ops vehicle that went down the runway about 20mins after DL 257 left"
- "One thing I would like to point out is how hard N195DN appeared to land on the right side before this departure..." (Picture of the previous landing)[
Combine this with the info from Avherald:
Delta Airlines said the crew was aware of tyre debris being found on the runway following their departure, Delta technicians however were unable to positively identify from photos whether the debris belonged to a Delta aircraft or not. The crew therefore declared emergency on approach to Sao Paulo as a precaution.
I think it's safe to assume that the crew hadn't noticed anything wrong with the TO roll, raised the gear normally, were informed later that tyre debris was found on the runway that
might have come from their A/C and therefore declared an emergency before ldg just in case.