Altitude bust, aircraft vibration.

Attributes
ACN	167663
Time
Date	199101
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dtw
State Reference	MI
Altitude	msl bound lower : 6500 msl bound upper : 7000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dtw
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other descent other
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 160 flight time total : 3850
ASRS Report	167663
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : overshoot inflight encounter other non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On our approach to dtw we were cleared from 11000' to 7000' by approach control. As were descending we experienced a violent vibration. Previous to this the air was very still. The vibration lasted for about 10-15 seconds. During the vibration we were unable to turn the aircraft with use of the ailerons. We experienced the same vibrations on 3 sep occasions on our descent to 7000', the last vibration occurring probably around 7500'. We felt that a control primary or secondary control was coming apart. After the first vibration we slowed the aircraft down. As we were both dealing with the problem at hand we descended below our assigned altitude of 7000'. We noticed the altitude at 6500' and immediately began a climb, at the same exact time ATC cleared us to 6000'. Nothing more was said by ATC. Because of both of our concentration fixated on the problem at hand our attention was drawn away from the altitude assignment. We reported our problem to ATC and they informed us that we were following an medium large transport and to be caution for wake turbulence. From this point the vibrations ceased. We felt that the vibrations were caused by wake turbulence, after inspecting the aircraft on the ground no problems were found.

Original NASA ASRS Text

Title: ALT BUST, ACFT VIBRATION.

Narrative: ON OUR APCH TO DTW WE WERE CLRED FROM 11000' TO 7000' BY APCH CTL. AS WERE DSNDING WE EXPERIENCED A VIOLENT VIBRATION. PREVIOUS TO THIS THE AIR WAS VERY STILL. THE VIBRATION LASTED FOR ABOUT 10-15 SECS. DURING THE VIBRATION WE WERE UNABLE TO TURN THE ACFT WITH USE OF THE AILERONS. WE EXPERIENCED THE SAME VIBRATIONS ON 3 SEP OCCASIONS ON OUR DSNT TO 7000', THE LAST VIBRATION OCCURRING PROBABLY AROUND 7500'. WE FELT THAT A CTL PRIMARY OR SECONDARY CTL WAS COMING APART. AFTER THE FIRST VIBRATION WE SLOWED THE ACFT DOWN. AS WE WERE BOTH DEALING WITH THE PROB AT HAND WE DSNDED BELOW OUR ASSIGNED ALT OF 7000'. WE NOTICED THE ALT AT 6500' AND IMMEDIATELY BEGAN A CLB, AT THE SAME EXACT TIME ATC CLRED US TO 6000'. NOTHING MORE WAS SAID BY ATC. BECAUSE OF BOTH OF OUR CONCENTRATION FIXATED ON THE PROB AT HAND OUR ATTN WAS DRAWN AWAY FROM THE ALT ASSIGNMENT. WE RPTED OUR PROB TO ATC AND THEY INFORMED US THAT WE WERE FOLLOWING AN MLG AND TO BE CAUTION FOR WAKE TURB. FROM THIS POINT THE VIBRATIONS CEASED. WE FELT THAT THE VIBRATIONS WERE CAUSED BY WAKE TURB, AFTER INSPECTING THE ACFT ON THE GND NO PROBS WERE FOUND.

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.