Certification
Quote from wileydog3:
An engine in reverse right after takeoff is going to be a challenge, no doubt. But again, one has to take the whole picture in view and consider flight test and certification. Do you think the FAA and JAA would certify an airplane and not consider the possibility of a reverser opening?
[Unquote]
Have never flown the MD-80 series, and have no Vmca or Vmcg figures. But Mad (Flt) Scientist has pointed out that manufacturers are unlikely to provide a rudder capability greater than is thought to be necessary, because of the possible penalties. stilton states that “most, if not all” the rudder will be required in what I’ve called a ‘normal’ engine failure, and wileydog3 seems to agree.
From the take-off certification point of view, I’m not aware that allowance has to be made for an engine failure that involves it producing reverse (negative) thrust of any degree. It is common on many types of aircraft, when light, to nominate a Vr (rotation) speed which is at or just above Vmca (particularly on contaminated runways). For the benefit of SLF3b and others, it needs to be pointed out that Vmca is the minimum control speed in the event of the failure of any one engine when airborne.
Regarding the Spanair accident, one assumes that it was relatively heavy, with a much higher rotate speed, so there would have been a considerable margin over Vmca. Whether that would be even theoretically sufficient to cater for reverser deployment − including the rudder-airflow problem − I’m not going to speculate.
In the event of spontaneous (faulty) reverser deployment, there is supposed to be an automatic selection of idle thrust, but turbofans take a significant time to slow down, and that probably includes even the old JT8D? Bucket-type reversers are old technology, and may be more prone to undesired deployment than the more modern (but less effective) fan reversers. Nevertheless, this would be an extremely rare event, and to happen at such a critical moment of the flight is not something one would expect the certification to take into account.