Narrative:

After takeoff from centennial airport runway 19L, the piper arrow I was flying did not reach a sufficient climb rate to safely clear obstacles in the vicinity of the airport, due to the failure of the landing gear to retract. I attempted to recycle the landing gear switch, but still could not retract the gear. By the time I realized the airplane was not going to climb, I was near the departure end of the runway with insufficient runway remaining to safely abort the takeoff. I declared an emergency to the tower, and was immediately cleared to land on any runway. I executed a shallow-banked turn to the left (over the southeast corner of the airport), at approximately 100 ft altitude, and landed on runway 35R. I later learned that a helipad is located on that area of the airport, and that during the left turn my airplane had come close to colliding with a light helicopter that was operating there. I did not see the helicopter during my maneuvering. I landed safely on runway 35R and taxied back to parking. Density altitude at the time of the emergency was approximately 7000 ft, and the airplane was loaded approximately 100 pounds below gross (pilot, 2 passenger, baggage, and partial fuel). According to performance charts the climb rate should have been approximately 300-400 FPM. The poh doesn't specify climb rates with the gear down, but during the emergency the climb rate was on the order of 50 FPM. A mechanic at centennial airport could find nothing wrong with the gear system, and was able to retract the gear. After reviewing the poh, I discovered that the automatic gear extension system on this airplane normally prevents the gear from retracting at an airspeed below 85 mph, but that this speed increases with increasing altitude. During subsequent experimentation I found that the required airspeed for gear retraction at this density altitude was approximately 105 mph, an airspeed that I never reached during the emergency. Several human factors contributed to this emergency. My passenger were in a hurry to get home, and we had attempted to leave denver from jefferson county airport earlier that day but were turned back by building thunderstorms and associated WX to the east. Had I decided to abort the takeoff earlier I could have easily landed on the remaining runway, but I was reluctant to do so because I had made a successful takeoff under similar conditions earlier the same day. I felt that I would be able to get the landing gear retracted, and that the airplane would then climb normally. Finally, I did not fully understand the operation of the automatic gear extension system, and specifically did not realize that the limiting retraction speed increased with altitude. Had I known this I would have activated the system override prior to takeoff.

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Original NASA ASRS Text

Title: PA28 PLT ALLOWED AUTOMATIC GEAR LOWERING SYS TO PREVENT GEAR RETRACTION, ON TKOF, AT A HIGH DENSITY ALT FIELD.

Narrative: AFTER TKOF FROM CENTENNIAL ARPT RWY 19L, THE PIPER ARROW I WAS FLYING DID NOT REACH A SUFFICIENT CLB RATE TO SAFELY CLR OBSTACLES IN THE VICINITY OF THE ARPT, DUE TO THE FAILURE OF THE LNDG GEAR TO RETRACT. I ATTEMPTED TO RECYCLE THE LNDG GEAR SWITCH, BUT STILL COULD NOT RETRACT THE GEAR. BY THE TIME I REALIZED THE AIRPLANE WAS NOT GOING TO CLB, I WAS NEAR THE DEP END OF THE RWY WITH INSUFFICIENT RWY REMAINING TO SAFELY ABORT THE TKOF. I DECLARED AN EMER TO THE TWR, AND WAS IMMEDIATELY CLRED TO LAND ON ANY RWY. I EXECUTED A SHALLOW-BANKED TURN TO THE L (OVER THE SE CORNER OF THE ARPT), AT APPROX 100 FT ALT, AND LANDED ON RWY 35R. I LATER LEARNED THAT A HELIPAD IS LOCATED ON THAT AREA OF THE ARPT, AND THAT DURING THE L TURN MY AIRPLANE HAD COME CLOSE TO COLLIDING WITH A LIGHT HELI THAT WAS OPERATING THERE. I DID NOT SEE THE HELI DURING MY MANEUVERING. I LANDED SAFELY ON RWY 35R AND TAXIED BACK TO PARKING. DENSITY ALT AT THE TIME OF THE EMER WAS APPROX 7000 FT, AND THE AIRPLANE WAS LOADED APPROX 100 LBS BELOW GROSS (PLT, 2 PAX, BAGGAGE, AND PARTIAL FUEL). ACCORDING TO PERFORMANCE CHARTS THE CLB RATE SHOULD HAVE BEEN APPROX 300-400 FPM. THE POH DOESN'T SPECIFY CLB RATES WITH THE GEAR DOWN, BUT DURING THE EMER THE CLB RATE WAS ON THE ORDER OF 50 FPM. A MECH AT CENTENNIAL ARPT COULD FIND NOTHING WRONG WITH THE GEAR SYS, AND WAS ABLE TO RETRACT THE GEAR. AFTER REVIEWING THE POH, I DISCOVERED THAT THE AUTOMATIC GEAR EXTENSION SYS ON THIS AIRPLANE NORMALLY PREVENTS THE GEAR FROM RETRACTING AT AN AIRSPD BELOW 85 MPH, BUT THAT THIS SPD INCREASES WITH INCREASING ALT. DURING SUBSEQUENT EXPERIMENTATION I FOUND THAT THE REQUIRED AIRSPD FOR GEAR RETRACTION AT THIS DENSITY ALT WAS APPROX 105 MPH, AN AIRSPD THAT I NEVER REACHED DURING THE EMER. SEVERAL HUMAN FACTORS CONTRIBUTED TO THIS EMER. MY PAX WERE IN A HURRY TO GET HOME, AND WE HAD ATTEMPTED TO LEAVE DENVER FROM JEFFERSON COUNTY ARPT EARLIER THAT DAY BUT WERE TURNED BACK BY BUILDING TSTMS AND ASSOCIATED WX TO THE E. HAD I DECIDED TO ABORT THE TKOF EARLIER I COULD HAVE EASILY LANDED ON THE REMAINING RWY, BUT I WAS RELUCTANT TO DO SO BECAUSE I HAD MADE A SUCCESSFUL TKOF UNDER SIMILAR CONDITIONS EARLIER THE SAME DAY. I FELT THAT I WOULD BE ABLE TO GET THE LNDG GEAR RETRACTED, AND THAT THE AIRPLANE WOULD THEN CLB NORMALLY. FINALLY, I DID NOT FULLY UNDERSTAND THE OP OF THE AUTOMATIC GEAR EXTENSION SYS, AND SPECIFICALLY DID NOT REALIZE THAT THE LIMITING RETRACTION SPD INCREASED WITH ALT. HAD I KNOWN THIS I WOULD HAVE ACTIVATED THE SYS OVERRIDE PRIOR TO TKOF.

Data retrieved from NASA's ASRS site as of July 2007 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.