A piper PA28 in cruise at 5000 ft declared an emergency and diverted due to the cabin door opening.

Attributes
ACN	530579
Time
Date	200111
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz.tracon
Operator	general aviation : personal
Make Model Name	PA-23-250 Aztec
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 17 flight time total : 1510 flight time type : 212
ASRS Report	530579
Person 2
Affiliation	government : faa
Function	controller : approach
Events
Anomaly	aircraft equipment problem : critical other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : diverted to another airport
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

During cruise flight, the cabin door popped open. An immediate high level of noise and a rolling moment similar to that experienced when an engine fails. A seemingly inadequate check of the check of the door by the PIC. Although the door passed a 'thump test' (bumping the door with a closed fist) and the door lock mechanism engaged, this was a false and inadequate locking. The PIC declared an emergency with ZZZ approach control as the flight characteristics were dramatically affected by the trailing open door. Landing was effected at ZZZ, united states. ZZZ traffic was using runway 31, when the PIC announced an emergency on unicom and he was landing straight in on runway 13 (opposite direction) due to handling instability of the aircraft, all aircraft in the ZZZ traffic pattern diverged away from the aircraft in distress and allowed a safe and uneventful landing. Once safely on the ground and clear of the runway, the door was examined for damage, the latching system tested and the door was re-secured. The flight continued uneventfully to ZZZ1 airport and finally to its home base, ZZZ2 airport. A maintenance squawk was made concerning the door and will be examined further and repaired as necessary by the amt.

Original NASA ASRS Text

Title: A PIPER PA28 IN CRUISE AT 5000 FT DECLARED AN EMER AND DIVERTED DUE TO THE CABIN DOOR OPENING.

Narrative: DURING CRUISE FLT, THE CABIN DOOR POPPED OPEN. AN IMMEDIATE HIGH LEVEL OF NOISE AND A ROLLING MOMENT SIMILAR TO THAT EXPERIENCED WHEN AN ENG FAILS. A SEEMINGLY INADEQUATE CHK OF THE CHK OF THE DOOR BY THE PIC. ALTHOUGH THE DOOR PASSED A 'THUMP TEST' (BUMPING THE DOOR WITH A CLOSED FIST) AND THE DOOR LOCK MECHANISM ENGAGED, THIS WAS A FALSE AND INADEQUATE LOCKING. THE PIC DECLARED AN EMER WITH ZZZ APCH CTL AS THE FLT CHARACTERISTICS WERE DRAMATICALLY AFFECTED BY THE TRAILING OPEN DOOR. LNDG WAS EFFECTED AT ZZZ, UNITED STATES. ZZZ TFC WAS USING RWY 31, WHEN THE PIC ANNOUNCED AN EMER ON UNICOM AND HE WAS LNDG STRAIGHT IN ON RWY 13 (OPPOSITE DIRECTION) DUE TO HANDLING INSTABILITY OF THE ACFT, ALL ACFT IN THE ZZZ TFC PATTERN DIVERGED AWAY FROM THE ACFT IN DISTRESS AND ALLOWED A SAFE AND UNEVENTFUL LNDG. ONCE SAFELY ON THE GND AND CLR OF THE RWY, THE DOOR WAS EXAMINED FOR DAMAGE, THE LATCHING SYS TESTED AND THE DOOR WAS RE-SECURED. THE FLT CONTINUED UNEVENTFULLY TO ZZZ1 ARPT AND FINALLY TO ITS HOME BASE, ZZZ2 ARPT. A MAINT SQUAWK WAS MADE CONCERNING THE DOOR AND WILL BE EXAMINED FURTHER AND REPAIRED AS NECESSARY BY THE AMT.

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.