Narrative:

I was captain and pilot flying of a lear 25 on an IFR flight plan. The mission was cargo transport and freight was aboard the aircraft. The flight departed after waiting several minutes in heavy rain and wind for safe takeoff weather. During this time the aircraft was oriented with the tail towards the wind. Once radar contact was established we were assigned a climb to 17000 ft and a radar vector. The rate of climb was approximately 4000 ft per minute. Shortly after takeoff the pitch trim clacker began brief intermittent soundings when no pitch trim input was being given. Due to moderate turbulence it was difficult to determine if any trim movement had taken place. I continued the climb with sensitivity to control pressure but could detect no unusual changes in trim; and the pitch trim worked normally when activated. I determined that the likely malfunction was in the annunciator system and that the trim was working normally. The last item of the after takeoff checklist which is a check of the cabin altitude. My first officer reported an abnormally high cabin altitude; but by this time we were passing through 10000 ft. Simultaneously; the cabin attendant altitude light illuminated. I immediately began to level off the aircraft; establishing level flight at 11000 ft. As I called for the cabin attendant altitude light checklist; the emergency pressurization system activated. This lowered the cabin altitude very quickly to about 5000 ft at which point emergency operation stopped and the cabin began to ride again towards our flight altitude at a rate of more than 4000 ft per minute. Just before donning oxygen I reported to ATC that we would be descending back to 10000 ft to address a pressurization issue; and ATC approved. The first officer began to read and perform the appropriate checklist with myself backing him up. During the course of completing the checklist; the cabin altitude fluctuated a great deal; resulting in one more activation of the emergency system. During these periods the noise level in the cockpit prevents communication with ATC. The cabin attendant altitude checklist indicates that if pressurization control is restored; flight may continue. This appeared to be the case. In accordance with the checklist I resumed my climb but limited the rate to 300 ft per minute. Again; when the aircraft reached 11000 ft the cabin altitude trend reversed and the emergency pressurization system was activated. At this point I decided to go back to ZZZ and descend; and intended to declare an emergency as soon as volume levels in the cockpit permitted. I believe both malfunctions may have been due in part to the conditions while holding for takeoff. Long exposure to high winds and water have affected electrical and pneumatic systems in my past experience with this type. ATC immediately approved a turn directly to ZZZ and a descent to 6000 ft. I began preparing the cockpit for the instrument approach while my officer searched for the airport. The pitch trim clacker was still intermittently sounding and the turbulence again become moderate as we descended. Shortly; we both had our attention divided by the approach checklist and the approach briefing which included extra material in consideration of the likelihood of windshear; the landing at near maximum landing weight on a wet runway in low ceiling conditions; and the operations specifications requirements for conducting operations to an airport with a closed control tower and no source of local weather. We were more than 25 miles away from the airport at the top of descent so there was no great rush; but in the midst of these tasks I became distracted and forgot to declare the emergency as I had intended. We requested vectors for a visual approach but did not see the airport until nearly on top of it. During vectors to re-acquire visual for the approach I entered a layer of low cloud that was below the MSA for the region; so I advised ATC that we were IMC and would need vectors to the ILS with a circle to the upwind runway (tower hadclosed; then a wind shift followed the storms and the runway being served by the active ILS was now downwind). Again; ATC immediately provided us with what we needed. The approach was made normally and the flight concluded. My first officer was able to perform all his required duties and more; but was later admitted to a nearby emergency room with ear injuries as a result of the pressure changes. My mistake in forgetting to declare an emergency and request of vectors to a visual with inadequate cloud clearance were both due to a high workload that was demanding but not so abnormal as to cause me to take delay action. I also resisted delay action because I suspected my first officer was in considerable pain and might need medical attention. Emergency authority may have reduced some of the workload.callback conversation with reporter revealed the following information: the reporter stated that the LR25 pressurization system is entirely pneumatic with the exception of a couple of microswitches. There was something in the system preventing the outflow valve from completely closing; thereby not allowing aircraft pressurization. When the cabin altitude of 10400 ft was reached; the emergency system; again entirely pneumatic; ported engine bleed air directly into the cabin thus causing a rapid pressure increase. This pressure change caused the first officer's ear distress. The trim alert the reporter believes was a false warning. Once on the ground; maintenance cleaned the pressurization system and it functioned normally. Nothing was found wrong with the trim system and to the reporter's knowledge it had not malfunctioned since this event. Likewise the pressurization functioned normally on the next flight.

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Original NASA ASRS Text

Title: AN LR25 HELD BEFORE TKOF IN WIND AND RAIN EXPERIENCED PITCH TRIM AND CABIN PRESSURIZATION ANOMALIES AFTER TKOF. THE FLT RETURNED TO LAND.

Narrative: I WAS CAPTAIN AND PILOT FLYING OF A LEAR 25 ON AN IFR FLIGHT PLAN. THE MISSION WAS CARGO TRANSPORT AND FREIGHT WAS ABOARD THE AIRCRAFT. THE FLIGHT DEPARTED AFTER WAITING SEVERAL MINUTES IN HEAVY RAIN AND WIND FOR SAFE TAKEOFF WEATHER. DURING THIS TIME THE AIRCRAFT WAS ORIENTED WITH THE TAIL TOWARDS THE WIND. ONCE RADAR CONTACT WAS ESTABLISHED WE WERE ASSIGNED A CLIMB TO 17000 FT AND A RADAR VECTOR. THE RATE OF CLIMB WAS APPROXIMATELY 4000 FT PER MINUTE. SHORTLY AFTER TAKEOFF THE PITCH TRIM CLACKER BEGAN BRIEF INTERMITTENT SOUNDINGS WHEN NO PITCH TRIM INPUT WAS BEING GIVEN. DUE TO MODERATE TURBULENCE IT WAS DIFFICULT TO DETERMINE IF ANY TRIM MOVEMENT HAD TAKEN PLACE. I CONTINUED THE CLIMB WITH SENSITIVITY TO CONTROL PRESSURE BUT COULD DETECT NO UNUSUAL CHANGES IN TRIM; AND THE PITCH TRIM WORKED NORMALLY WHEN ACTIVATED. I DETERMINED THAT THE LIKELY MALFUNCTION WAS IN THE ANNUNCIATOR SYSTEM AND THAT THE TRIM WAS WORKING NORMALLY. THE LAST ITEM OF THE AFTER TAKEOFF CHECKLIST WHICH IS A CHECK OF THE CABIN ALTITUDE. MY FIRST OFFICER REPORTED AN ABNORMALLY HIGH CABIN ALTITUDE; BUT BY THIS TIME WE WERE PASSING THROUGH 10000 FT. SIMULTANEOUSLY; THE CAB ALT LIGHT ILLUMINATED. I IMMEDIATELY BEGAN TO LEVEL OFF THE AIRCRAFT; ESTABLISHING LEVEL FLIGHT AT 11000 FT. AS I CALLED FOR THE CAB ALT LIGHT CHECKLIST; THE EMERGENCY PRESSURIZATION SYSTEM ACTIVATED. THIS LOWERED THE CABIN ALTITUDE VERY QUICKLY TO ABOUT 5000 FT AT WHICH POINT EMERGENCY OPERATION STOPPED AND THE CABIN BEGAN TO RIDE AGAIN TOWARDS OUR FLIGHT ALTITUDE AT A RATE OF MORE THAN 4000 FT PER MINUTE. JUST BEFORE DONNING OXYGEN I REPORTED TO ATC THAT WE WOULD BE DESCENDING BACK TO 10000 FT TO ADDRESS A PRESSURIZATION ISSUE; AND ATC APPROVED. THE FIRST OFFICER BEGAN TO READ AND PERFORM THE APPROPRIATE CHECKLIST WITH MYSELF BACKING HIM UP. DURING THE COURSE OF COMPLETING THE CHECKLIST; THE CABIN ALTITUDE FLUCTUATED A GREAT DEAL; RESULTING IN ONE MORE ACTIVATION OF THE EMERGENCY SYSTEM. DURING THESE PERIODS THE NOISE LEVEL IN THE COCKPIT PREVENTS COMMUNICATION WITH ATC. THE CAB ALT CHECKLIST INDICATES THAT IF PRESSURIZATION CONTROL IS RESTORED; FLIGHT MAY CONTINUE. THIS APPEARED TO BE THE CASE. IN ACCORDANCE WITH THE CHECKLIST I RESUMED MY CLIMB BUT LIMITED THE RATE TO 300 FT PER MINUTE. AGAIN; WHEN THE AIRCRAFT REACHED 11000 FT THE CABIN ALTITUDE TREND REVERSED AND THE EMERGENCY PRESSURIZATION SYSTEM WAS ACTIVATED. AT THIS POINT I DECIDED TO GO BACK TO ZZZ AND DESCEND; AND INTENDED TO DECLARE AN EMERGENCY AS SOON AS VOLUME LEVELS IN THE COCKPIT PERMITTED. I BELIEVE BOTH MALFUNCTIONS MAY HAVE BEEN DUE IN PART TO THE CONDITIONS WHILE HOLDING FOR TAKEOFF. LONG EXPOSURE TO HIGH WINDS AND WATER HAVE AFFECTED ELECTRICAL AND PNEUMATIC SYSTEMS IN MY PAST EXPERIENCE WITH THIS TYPE. ATC IMMEDIATELY APPROVED A TURN DIRECTLY TO ZZZ AND A DESCENT TO 6000 FT. I BEGAN PREPARING THE COCKPIT FOR THE INSTRUMENT APPROACH WHILE MY OFFICER SEARCHED FOR THE AIRPORT. THE PITCH TRIM CLACKER WAS STILL INTERMITTENTLY SOUNDING AND THE TURBULENCE AGAIN BECOME MODERATE AS WE DESCENDED. SHORTLY; WE BOTH HAD OUR ATTENTION DIVIDED BY THE APPROACH CHECKLIST AND THE APPROACH BRIEFING WHICH INCLUDED EXTRA MATERIAL IN CONSIDERATION OF THE LIKELIHOOD OF WINDSHEAR; THE LANDING AT NEAR MAX LANDING WEIGHT ON A WET RUNWAY IN LOW CEILING CONDITIONS; AND THE OPERATIONS SPECIFICATIONS REQUIREMENTS FOR CONDUCTING OPERATIONS TO AN AIRPORT WITH A CLOSED CONTROL TOWER AND NO SOURCE OF LOCAL WEATHER. WE WERE MORE THAN 25 MILES AWAY FROM THE AIRPORT AT THE TOP OF DESCENT SO THERE WAS NO GREAT RUSH; BUT IN THE MIDST OF THESE TASKS I BECAME DISTRACTED AND FORGOT TO DECLARE THE EMERGENCY AS I HAD INTENDED. WE REQUESTED VECTORS FOR A VISUAL APPROACH BUT DID NOT SEE THE AIRPORT UNTIL NEARLY ON TOP OF IT. DURING VECTORS TO RE-ACQUIRE VISUAL FOR THE APPROACH I ENTERED A LAYER OF LOW CLOUD THAT WAS BELOW THE MSA FOR THE REGION; SO I ADVISED ATC THAT WE WERE IMC AND WOULD NEED VECTORS TO THE ILS WITH A CIRCLE TO THE UPWIND RUNWAY (TOWER HADCLOSED; THEN A WIND SHIFT FOLLOWED THE STORMS AND THE RUNWAY BEING SERVED BY THE ACTIVE ILS WAS NOW DOWNWIND). AGAIN; ATC IMMEDIATELY PROVIDED US WITH WHAT WE NEEDED. THE APPROACH WAS MADE NORMALLY AND THE FLIGHT CONCLUDED. MY FIRST OFFICER WAS ABLE TO PERFORM ALL HIS REQUIRED DUTIES AND MORE; BUT WAS LATER ADMITTED TO A NEARBY EMERGENCY ROOM WITH EAR INJURIES AS A RESULT OF THE PRESSURE CHANGES. MY MISTAKE IN FORGETTING TO DECLARE AN EMERGENCY AND REQUEST OF VECTORS TO A VISUAL WITH INADEQUATE CLOUD CLEARANCE WERE BOTH DUE TO A HIGH WORKLOAD THAT WAS DEMANDING BUT NOT SO ABNORMAL AS TO CAUSE ME TO TAKE DELAY ACTION. I ALSO RESISTED DELAY ACTION BECAUSE I SUSPECTED MY FO WAS IN CONSIDERABLE PAIN AND MIGHT NEED MEDICAL ATTENTION. EMERGENCY AUTHORITY MAY HAVE REDUCED SOME OF THE WORKLOAD.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT THE LR25 PRESSURIZATION SYSTEM IS ENTIRELY PNEUMATIC WITH THE EXCEPTION OF A COUPLE OF MICROSWITCHES. THERE WAS SOMETHING IN THE SYSTEM PREVENTING THE OUTFLOW VALVE FROM COMPLETELY CLOSING; THEREBY NOT ALLOWING ACFT PRESSURIZATION. WHEN THE CABIN ALT OF 10400 FT WAS REACHED; THE EMERGENCY SYSTEM; AGAIN ENTIRELY PNEUMATIC; PORTED ENG BLEED AIR DIRECTLY INTO THE CABIN THUS CAUSING A RAPID PRESSURE INCREASE. THIS PRESSURE CHANGE CAUSED THE FO'S EAR DISTRESS. THE TRIM ALERT THE REPORTER BELIEVES WAS A FALSE WARNING. ONCE ON THE GROUND; MAINTENANCE CLEANED THE PRESSURIZATION SYSTEM AND IT FUNCTIONED NORMALLY. NOTHING WAS FOUND WRONG WITH THE TRIM SYSTEM AND TO THE REPORTER'S KNOWLEDGE IT HAD NOT MALFUNCTIONED SINCE THIS EVENT. LIKEWISE THE PRESSURIZATION FUNCTIONED NORMALLY ON THE NEXT FLIGHT.

Data retrieved from NASA's ASRS site as of May 2009 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.