Altitude deviation altitude excursion - mountain wave activity.

Attributes
ACN	295348
Time
Date	199502
Day	Wed
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : den
State Reference	CO
Altitude	msl bound lower : 30600 msl bound upper : 31000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute airway : zdc
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 6000 flight time type : 2500
ASRS Report	295348
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : exited adverse environment flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

We had been searching for a smooth ride (FL280, FL260, then FL310) when the turbulence went from occasional moderate to continuous moderate. As we crossed the frontal range it immediately smoothed out and we attempted to get back to our desired cruise speed (.84 mach). As our speed increased to about .82 mach we were hit with solid moderate turbulence. Our airspeed jumped right up and as we throttled back the autoplt started struggling to hold altitude. I reported to ZDV that we were struggling to hold altitude plus or minus 250 ft. He said no problem as there was no conflicting traffic. We thought the autoplt had settled down when the wave took us down even further. The captain then disconnected and I reported to denver that we were now - 400 ft. As soon as we steadied the aircraft the wave stopped as well as the turbulence. ZDV was helpful by advising other aircraft of our position and what we experienced-moderate turbulence and mountain wave.

Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION - MOUNTAIN WAVE ACTIVITY.

Narrative: WE HAD BEEN SEARCHING FOR A SMOOTH RIDE (FL280, FL260, THEN FL310) WHEN THE TURB WENT FROM OCCASIONAL MODERATE TO CONTINUOUS MODERATE. AS WE CROSSED THE FRONTAL RANGE IT IMMEDIATELY SMOOTHED OUT AND WE ATTEMPTED TO GET BACK TO OUR DESIRED CRUISE SPD (.84 MACH). AS OUR SPD INCREASED TO ABOUT .82 MACH WE WERE HIT WITH SOLID MODERATE TURB. OUR AIRSPD JUMPED RIGHT UP AND AS WE THROTTLED BACK THE AUTOPLT STARTED STRUGGLING TO HOLD ALT. I RPTED TO ZDV THAT WE WERE STRUGGLING TO HOLD ALT PLUS OR MINUS 250 FT. HE SAID NO PROB AS THERE WAS NO CONFLICTING TFC. WE THOUGHT THE AUTOPLT HAD SETTLED DOWN WHEN THE WAVE TOOK US DOWN EVEN FURTHER. THE CAPT THEN DISCONNECTED AND I RPTED TO DENVER THAT WE WERE NOW - 400 FT. AS SOON AS WE STEADIED THE ACFT THE WAVE STOPPED AS WELL AS THE TURB. ZDV WAS HELPFUL BY ADVISING OTHER ACFT OF OUR POS AND WHAT WE EXPERIENCED-MODERATE TURB AND MOUNTAIN WAVE.

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.