Why would you want a flight lock?
Not all emergency doors are of plug-type. It would be disastrous if someone opened a non-plug door mid-flight, so fail-safe locks are required to secure them.
FAR 23.807 - Emergency Exits
(d)(2) A means must be provided to lock each emergency exit and to safeguard against its opening in flight, either inadvertently by persons or as a result of mechanical failure. In addition, a means for direct visual inspection of the locking mechanism must be provided to determine that each emergency exit for which the initial opening movement is outward is fully locked.