B737-700
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
Aircraft Equipment Problem Critical
General Flight Cancelled / Delayed; General Maintenance Action
Procedure; Aircraft
We had just finished the Before Start Checklist and the Flight Attendant just closed the flight deck door and checked to make sure it was closed. The door switch was down and all lights on the center panel were out. However; I always go beyond the call of duty and push on the door from the inside to make sure it is closed. When I did so; the door came flying open. The metal door lock inside the frame was not locking. We MEL'd it with Maintenance and were told to use the manual lock instead.I have had this happen three times in my career where the door lock fails like this. I have filed reports about this problem before and nothing has been done to fix this safety threat with the way we do things here at Company. Our checklist tells us to look at the lights on the center panel to see if they are out. For some reason we seem to think those lights are telling us that the metal latch inside the door is actually working right; but that is wrong. That LOCK FAIL light is only telling me that [the] electrical power circuitry in the arming switch portion of the door is indicating that the Flight Deck Access System Switch is off; or the flight deck door has failed to lock. However; we have seen that it does not always detect a failed door lock working properly. We have seen that flight deck doors come open with the LOCK FAIL light and the AUTO UNLK lights both out and the arming switch is in the downed position. Nowhere in our procedures does it tell a Pilot to physically push on the door from inside the flight deck to double check to make sure the lock is actually working; to make sure the door does not fly open. About 90 percent of the time Flight Attendants do not check the door or forget to flip the switch down when they close the door. I have caught many times that the door was not locked properly by just pushing on it and having it come open. We are letting our guard down and accepting too much risk by not adding in our procedures; or including in our checklist to have either Pilot take one second and push on the door from the inside to make sure it is indeed locked and working properly. This is the only airline I have ever flown for that does not physically push on the door to make sure it is secure. We need to add this to our procedure.
B737-700 First Officer reported a recurring failure of cockpit door locking mechanism and the incorrect door locking procedures.