2011-09 · NASA ASRS report 973041
A B717 Panel Data Concentrator Unit (PDCU) failed at FL330 causing NAV; autoflight and pressurization system failures so an emergency was declared; the QRH complied with and the flight diverted to a nearby airport.
Flight progressed normally from preflight through approximately one hour into the flight at cruise altitude FL330; in NAV mode. As pilot flying; I witnessed the aircraft spontaneously revert to heading mode (HDG flashing). Immediately following this event; the display units filled with amber alerts; nearly all numeric readouts were replaced with amber X's; and nearly all SDCP cue switches illuminated. Attempts to return to NAV mode using the NAV button were unsuccessful. The Captain immediately ordered that I don my O2 mask. We declared an emergency and descended. During descent; the Captain assumed control of the aircraft while I consulted the QRH for the Cabin Altitude emergency checklist. We notified the lead Flight Attendant; and informed the passengers of a pressurization problem and our imminent arrival into a nearby divert airport; which was approximately 80 NM to the northeast. We then obtained the destination weather; set up the approach; ran the In Range checklist; and calculated our landing weight to be within limits (the quantity of fuel used was one of very few numbers remaining on our displays). We asked for a gradual descent from 10;000 FT; as we were; by then; unpressurized; having heard the aural 'cabin altitude' alert at approximately 11;500 FT. We landed on Runway 36 and taxied to the gate.
Enroute the First Officer's Nav went to flashing heading mode and the EAD lit up full of alerts. When the Status page was selected; a full screen; (over 20); of alerts were present. Also; I had a sensation that the cabin might be climbing. I checked the secondary engine screen where cabin altitude and rate are annotated; and there were amber X's. I selected the air cue page and it was full of amber X's - no information. I checked the ELEC page and all buses were powered (green). I checked the circuit breaker panels and none were popped. Again I had the sensation that the cabin was climbing; but we had no information to confirm this. I told the First Officer we were depressurizing and to don O2 masks. I took the airplane; had the First Officer declare an emergency; get a descent to 10;000 FT; and tell ATC we were diverting. The First Officer took the airplane while I talked to the flight attendants and passengers. The Cabin Altitude alert came on passing 12;000 FT. As slats and flaps were extended we paid attention to the proper sounds and pitch changes; as we could not count on visual confirmation. Upon arrival; all passengers deplaned. We departed for our planned destination on another airplane with all passengers aboard.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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