1st why did the Capt decide to keep the passengers/crew in the air for 4 hrs obviously getting very worried when a dump of fuel takes approx. 50mins and a return to Gatwick would take whatever from the point of the problem starting (after take off?)
You'll need to wait until a report (if there is one) comes out. However, 2 things spring to mind:
- Fuel Dump is intended to get aircraft down to MLW, and some tanks cannot be dumped in some aircraft (not sure about 744?). In some emergencies, you then want to burn more to get to minimum weight/fuel which takes time. Clearly this was not a "time critical" issue.
- The nature of the problem will be assessed by airline and Boeing engineers for potential solutions. This takes time, and worth giving them the maximum possible.