It would appear that the CDLS 'LOCK' mode prevented the cockpit door being opened using the emergency access method.
2 crew members at all times in the cockpit is one solution; however, would it not be reasonable to change the CDLS so that selecting the 'LOCK' mode requires dual consent? Fit 2 pushbuttons in physical locations that cannot be reached by a single occupant, with a logic requiring that both have to be operated together before the CDLS 'LOCK' is activated - one CM must push and hold the 'consent' pushbutton on one side, then the other CM must press the other 'consent' pushbutton to enable the CDLS 'LOCK'.
Probably an expensive modification, but not unreasonable for an aircraft operator who does not require the cockpit to be fully manned at all times. Whether it's simpler to use sufficiently competent cockpit babysitters whenever one pilot needs to leave the cockpit is open to doubt - as that would probably incur training costs.
Last edited by BEagle; 27th Mar 2015 at 07:21.