- Other than a birdstrike, is there anything else which would explain the loud thud and then vibration on departure?
- Is it normal to take a decision that not only a birdstrike has occurred, but to divert the aircraft, only to change your mind?
- What are the chances that the crew involved would be able to explain what actually happened?!
1. There could indeed be other reasons, but let's leave details of those untouched in this discussion, as you are asking an operational question rather then a technical detailed one;
2. Let's be clear, a
suspected bird strike occurred, which may (or not) have happened inside the airport perimeter, thus ATC can possibly only comment on the speculation in case it may have been within.
3. Little chance...
However in general, for the non flight crew reading this forum including OP:
Initial crew actions would involve evidence gathering, which would include a more closer look at existing engine parameters, possible asking cabin crew if any smells were observed during or immediately after the event, ensuring all extended flaps and slats have retracted to en-route configuration without problem, etc.
If no smells were observed then there is a reasonably good chance that any suspected birds may have missed the engine core, thus not damaging the internal of the propulsion systems.
If no vibrations above and beyond those expected during flight are recorded by the engine instruments AND there is no significant increase in vibrations during further climb it would indicate nil or little fan blade damage has occurred if it has been struck. The front fan [indicated at %N1 on the engine instrument panel for pilots to see] on the engine will rotate faster in thinner air aloft, thus if there would be any damage to one or a few of its fan blades, vibration would soon become very high when the engine is used at full climb power, requiring the crew to reduce engine power to remain within limits, this would likely result in a diversion subsequently.
If all extended devices (slats and flaps) have been fully retracted then there is no indication of damage to the extension/retraction mechanism, thus the aircraft is configured for en-route flight.
Operational discussion points then would include (but are not limited to) if it would be more sensible to land with a relatively high (possibly over maximum landing) weight at a destination offering a suitable runway which has subsequent required engineering cover, or to continue to a different suitably equipped airfield further afield, or to continue to intended destination if all parameters are within limits.
Contacting Engineering and/or Operations can assist in such decision making, as they can assist in diagnosis and advise of engineering cover [Engineering] and may have additional information which may not be pertinent to the aircrew [Operations], including advice on relevant NOTAMs, available handling agents and/or strikes, information of which may not be required to be carried by crew for such suitable diversion airports as part of the preflight briefing package (contrary to some passenger belief, aircrew do not carry all NOTAMs for all airfield in Europe thus may not be aware of any imposed unless questioning this).
An initial decision of aircrew to divert after such event may have been fuelled by simulator training and expectation. However having consulted with engineers they may well have reassessed such decision and review such requirement.
In the process of decision making crews are there to ensure a safe flight, using all available resources to come to a decision and define a course of action. This decision making model is a fluid and continuous process which will be reviewed at each finding of evidence or additional piece of information.
Ultimately, airlines and its crews are ensuring to achieve "happy" passengers having arrived at their destination safely.