BAe 125 Series 800
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution
Aircraft
During initial climb out and normal power changes we observed large fluctuations between 1;500 and 2;000 FT per minute on the Cabin Rate indicator. We also felt and heard abnormal changes in the cabin pressurization. After a brief ATC level off at 6;000 FT we were given further climb to 17;000. Upon advancing the power the main air valve 2 annunciator illuminated. We then accomplished the abnormal checklist which resolved the annunciator. We then manipulated the throttles and illuminated the same annunciator. We were unable to control the cabin rate with the cabin rate control knob throughout the event. The decision was made to return to the point of departure with a hold first to assure an under weight landing. The flight was completed without further events or complications. I do not believe that this event was preventable due to the nature of a mechanical failure. We reached a safe and positive outcome with good CRM; positive discussion; and coordination though crew and ATC.
Hawker 800 experiences erratic cabin pressurization during initial climb. Attempts to control pressurization manually are unsuccessful and the crew elects to return to the departure airport.