Narrative:

During preparation for departure we noted a baggage door open cas message. When on site maintenance was unable to correct the discrepancy we completed appropriate MEL action. Subsequently; during engine start; we noted the baggage door seal cas message. We again conferred with local maintenance and completed the MEL deferral procedure for the baggage door seal. The MEL did not specifically direct reconfiguration of any cockpit switches. We subsequently departed and during climbout; while conducting the after takeoff checklist; noted an amber cabin altitude message followed quickly by the red cabin altitude message. We reduced the climb rate and requested a descent to 10;000 ft as well as a delay vector for troubleshooting. The crew reviewed the emergency checklist and noted the step to activate the iso [baggage compartment isolation valve] switch if cabin altitude had not been controlled. After doing so the cabin altitude was brought under control. We discussed our options and; although we suspected that the baggage isolation was the cause of the problem; elected to return to our departure airport due to the presence of on site maintenance. The crew coordinated with ATC and completed an uneventful return.we had reviewed the baggage door seal MEL with maintenance before departing. We believed that the baggage compartment would be automatically isolated. Apparently; further investigation might have prompted us to activate the iso valve switch before departure. The MEL mentions altitude limitations as well as limits on flights with the baggage compartment unpressurized; but did not direct closing of the switch. The maintenance personnel indicated that the type of baggage door switch installed on our aircraft was different and may have prevented the baggage compartment from isolating automatically.

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Original NASA ASRS Text

Title: Confusion over the wording of a pressurization MEL item caused the flight crew of a C-750 to takeoff; expecting the baggage compartment ISO (Isolation valve) to close automatically at 1.0 psi differential pressure. When it did not do so they returned to their departure airport for maintenance.

Narrative: During preparation for departure we noted a Baggage Door Open CAS message. When on site Maintenance was unable to correct the discrepancy we completed appropriate MEL action. Subsequently; during engine start; we noted the BAGGAGE DOOR SEAL CAS message. We again conferred with Local Maintenance and completed the MEL deferral procedure for the Baggage Door Seal. The MEL DID NOT specifically direct reconfiguration of any cockpit switches. We subsequently departed and during climbout; while conducting the After Takeoff Checklist; noted an amber Cabin Altitude message followed quickly by the Red Cabin Altitude message. We reduced the climb rate and requested a descent to 10;000 FT as well as a delay vector for troubleshooting. The crew reviewed the Emergency Checklist and noted the step to activate the ISO [baggage compartment ISOLATION Valve] switch if cabin altitude had not been controlled. After doing so the cabin altitude was brought under control. We discussed our options and; although we suspected that the baggage isolation was the cause of the problem; elected to return to our departure airport due to the presence of on site Maintenance. The crew coordinated with ATC and completed an uneventful return.We had reviewed the Baggage Door Seal MEL with Maintenance before departing. We believed that the baggage compartment would be automatically isolated. Apparently; further investigation might have prompted us to activate the ISO Valve switch before departure. The MEL mentions altitude limitations as well as limits on flights with the baggage compartment unpressurized; but did not direct closing of the switch. The Maintenance personnel indicated that the type of Baggage Door Switch installed on our aircraft was different and may have prevented the baggage compartment from isolating automatically.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.