B737 Undifferentiated or Other Model
Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Security
General Maintenance Action
Aircraft
Recently I was waiting at the cockpit door to receive a cup of coffee from the 'A' Flight Attendant. I reached up to check the manual cockpit door lock. I was surprised to find that I could not lock the cockpit door manually in the event of a lockdown. I tried pulling on the strap inward and still could not lock the door manually. When we got on the ground; I called Maintenance to the cockpit. The Mechanic tried to push on the upper part of the door from the forward galley. Even with his outside pressure; the deadbolt would not penetrate the door frame receiver. Eventually; the Mechanic had to adjust the door frame receiver to allow the deadbolt in.Since then (approximately 30 days ago) I have found four other aircraft with basically the same problem. Two of them I was able to get the cockpit door locked enroute but had to pull very hard on the strap. Would I have the time or the forethought to do this in an actual emergency? My thoughts: I think over the past 12 years; the cockpit doors are prone to shifting based on temperature changes and twisting movements from the aircraft. This might be causing some deadbolts to align offset causing the problem. This worries me.  Hopefully a check can be performed by Maintenance while on the ground and one in the air to adjust everything to allow a quick lockdown should one be needed.
A B737 pilot discovered that he was unable to lock down the flight station door using the manual cockpit door lock while in-flight. Maintenance adjusted that door frame receiver but the reporter later found several other aircraft with same problem.