A B767 in descent at 17000 ft was found to have a short duration pulse of one half second in pitch.

Attributes
ACN	673762
Time
Date	200509
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 17000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz.tracon
Operator	common carrier : air carrier
Make Model Name	B767 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : atp
Experience	flight time last 90 days : 170 flight time total : 11150 flight time type : 4050
ASRS Report	673762
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : unable
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

The B767-300 performed flawlessly until the descent. I was the PF and we were about 300 KIAS when the first officer commented about a sensation he felt in the yoke while pressing the microphone switch to transmit. The autoplt was engaged; so I had not felt it. I rested my hand lightly on the yoke and noticed an intermittent; short duration pulse of about 1/2 second duration. Passing 17000 ft MSL; I disconnected the autoplt; and at irregular intervals; usually 3-5 mins apart or more; I felt the very slight pulse in pitch only. All other control forces were normal; but the sensation was noticed at airspds as low as 170 KIAS during the approach. The landing and rollout were uneventful; and maintenance was contacted after landing. Logbook entry was made describing the event; and a mechanic was briefed by the flight crew at the gate.

Original NASA ASRS Text

Title: A B767 IN DSCNT AT 17000 FT WAS FOUND TO HAVE A SHORT DURATION PULSE OF ONE HALF SECOND IN PITCH.

Narrative: THE B767-300 PERFORMED FLAWLESSLY UNTIL THE DSCNT. I WAS THE PF AND WE WERE ABOUT 300 KIAS WHEN THE FO COMMENTED ABOUT A SENSATION HE FELT IN THE YOKE WHILE PRESSING THE MIKE SWITCH TO XMIT. THE AUTOPLT WAS ENGAGED; SO I HAD NOT FELT IT. I RESTED MY HAND LIGHTLY ON THE YOKE AND NOTICED AN INTERMITTENT; SHORT DURATION PULSE OF ABOUT 1/2 SECOND DURATION. PASSING 17000 FT MSL; I DISCONNECTED THE AUTOPLT; AND AT IRREGULAR INTERVALS; USUALLY 3-5 MINS APART OR MORE; I FELT THE VERY SLIGHT PULSE IN PITCH ONLY. ALL OTHER CTL FORCES WERE NORMAL; BUT THE SENSATION WAS NOTICED AT AIRSPDS AS LOW AS 170 KIAS DURING THE APCH. THE LNDG AND ROLLOUT WERE UNEVENTFUL; AND MAINT WAS CONTACTED AFTER LNDG. LOGBOOK ENTRY WAS MADE DESCRIBING THE EVENT; AND A MECH WAS BRIEFED BY THE FLT CREW AT THE GATE.

Data retrieved from NASA's ASRS site as of January 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.