Dash 8-400
Flight Crew Commercial
Distraction; Situational Awareness; Troubleshooting
Aircraft Equipment Problem Less Severe
Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; General Release Refused / Aircraft Not Accepted; General Maintenance Action
Aircraft
We made the decision to return to the departure airport. As we passed through 10;000 FT the Captain and I heard a loud hissing and vibrating sound that seemed to be coming from the cockpit escape hatch. The sound lasted only a few seconds and we promptly called by the Flight Attendants asking if they had heard the sound as well and how the passengers were doing. They told us that some of the forward passengers had heard noise and that it seemed to come from the Main Cabin door. At this point we had begun a descent back to 10;000 FT and slowed to 200 KTS. During the descent we checked the pressurization several times and it seemed to be holding the correct pressure. As the power was decreased for the descent and to slow down; we heard the noise again and could hear the packs surging as they adjusted for the new power setting. We referenced the QRH for the problem; but there was not a corresponding checklist. The Captain then called Maintenance and informed them of the situation and then called Dispatch through [a commercial radio service]. The Captain and Dispatch collectively decided that returning to the departure airport was the best course of action. No emergency was declared [but] Tower had chosen to dispatch the fire and rescue trucks as an additional precaution. We landed the aircraft without incident and returned to gate where the aircraft could be further inspected.
We did not suspect any structural damage or safety issues and thus did not declare an emergency; however the Tower out of precaution rolled the trucks (there was an emergency aircraft landing about 5 minutes after us). Swapped airplanes and arrived in our planned destination later that night.
A Q400 main cabin door developed a loud hissing noise and vibration at about 10;000 FT so the crew returned to the departure airport as a precaution although pressurization remained normal.