There are two interesting regulatory issues arising from this incident:
1. AAIB/FAA etc. recommendations versus ADs. This seems to be an instance where, in retrospect, one would wish that an AD had been issued following previous similar incidents. One wonders why this didn't happen, given that a double cowl separation could easily arise from a single maintenance/inspection SNAFU and could fatally compromise twin-engine redundancy.
2. What actions operators should take in the time lag between the AAIB starting its investigation and publication of its report. To give one example (which sadly involved friends of mine): in July 2009 a four year old girl fell through the railings at the top of the integral airstairs of a RYR 737-800 at STN. There was an AAIB investigation leading to a
report which was published just over a year later in August 2010. This time lag was unfortunately too great to prevent a recurrence of exactly the same incident to another little girl at
Girona in June 2010.
There is anecdotal evidence on this board of operators taking immediate action to tighten their procedures - and their engine cowls. And there is a wide spectrum between incidents which require a whole fleet to be grounded immediately (e.g. 787 batteries) and stuff which can be kicked into next year. But the two Ryanair incidents show that operators can't be relied upon to get things right prior to the regulator's report and recommendation - so perhaps more is required from the regulators in the interim?
(Finally - please don't jump on the fact that I've mentioned two RYR incidents. I'm sure there are similar 'regulatory lag' examples out there involving other operators.)