NTSB Identification: LAX86MA275.
The docket is stored on NTSB microfiche number 32629.
Scheduled 14 CFR UNITED AIRLINES
Incident occurred Tuesday, June 24, 1986 in PACIFIC OCEAN
Aircraft: BOEING 747-122, registration: N4718U
Injuries: 436 Uninjured.

NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft accident report.

WHILE UAL FLT 1 WAS CRUISING AT FL 310, APRX 1.8 HR AFTER TAKEOFF, A FLT ATTENDANT (F/A) RPRTD A HEADACHE & LIGHTHEADED-NESS. THE FLT CLIMBED TO FL 350, THEN ANOTHER F/A & SVRL PAX RPRTD SIMILAR SYMPTOMS. AT THAT TIME, THE TROPOPAUSE WAS AT40,000'. AS THE FLT CONTD, THE TROPOPAUSE LOWERED SOME, THEN INCREASED IN ALT. SUBSEQUENTLY, SVRL OTHER OCCUPANTS HAD SIMILAR SYMPTOMS. THE CAPT TURNED ON THE 'NO SMOKING' SIGN AS A PSBL SOLUTION, BUT THIS DID NOT SEEM TO HELP. NO HAZARD-OUS CARGO LEAK WAS FND & NO PAX ADMITTED CARRYING BUTANE OR OTHER SUCH SUBSTANCE. THOSE AFFECTED BY THE PSBL IRRITATING OR GASEOUS SUBSTANCE WERE IN ZONES B, C, D, E OR THE UPPER DECK OF THE ACFT. NO OCCUPANTS OF ZONE A OR THE FLT DECK WEREAFFECTED, EXCEPT THE 2ND OFFICER RPRTD A SLIGHT PAIN BETWEEN HIS EYEBROWS AFTER SPENDING 10 TO 20 MIN IN THE PAX CABIN. AN INVESTIGATION FOR A POSSIBLE OZONE ENCOUNTER WAS MADE, BUT NO SPECIFIC EVIDENCE WAS FOUND. THE CATALYTIC CONVERTERS IN THE AIR CONDITIONING SYS WERE TESTED & FOUND TO BE 51.2% EFFICIENT.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

REASON FOR OCCURRENCE UNDETERMINED

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

FUSELAGE,CABIN..OTHER


Contributing Factors

AIR COND/HEATING/PRESSURIZATION..BLOCKED(PARTIAL)

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