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37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
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Pms in medium large transport was making large change in power. Strong wave action present. PF thought he could do better and went to manual and lost 300'. Returned to assigned altitude.
| Attributes | |
| ACN | 101468 |
| Time | |
| Date | 198901 |
| Day | Fri |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : als |
| State Reference | NM |
| Altitude | msl bound lower : 36700 msl bound upper : 37000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zab artcc : zla |
| Operator | common carrier : air carrier |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Navigation In Use | Other |
| Flight Phase | cruise other |
| Route In Use | enroute airway : zab |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 200 flight time total : 7500 flight time type : 400 |
| ASRS Report | 101468 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude non adherence : clearance |
| Independent Detector | other controllera other flight crewa |
| Resolutory Action | flight crew : returned to intended course or assigned course flight crew : regained aircraft control other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
During cruise at FL370 in medium large transport with pms controling the autothrottles, we encountered wave action which caused the throttles to go all the way from 1.22 to 2.03 EPR. I thought I could make a better ride west/O the large power changes being made by pms so I turned the autothrottles off and reduced the EPR to 1.8. After checking speed to make sure it didn't bleed off I noticed the pitch window of the FMA was reading mach instead of altitude hold. As I reached to touch the altitude hold button the altitude alert warned 'altitude.' I disconnected the autoplt added power and got right smartly back to FL370 from FL367. As we approached FL370 within 50' the controller asked us to confirm we were at FL370 which we did since we were there again. I'm sure his switch went off since we were within 2-3 mi of crossing traffic at FL350. Human performance considerations: although the training at my carrier is excellent I feel I was let down here. A book on pms and some discussion of pms on my log didn't cut it. I also feel this is a design flaw. Turning autothrottles off should not cause you to lose the altitude hold function. Instead of failing from performance cruise to mach it should fail from performance cruise to altitude hold. New generation electronics are wonderful but the monitoring workload is considerable and I hate finding the built in traps this way.
Original NASA ASRS Text
Title: PMS IN MLG WAS MAKING LARGE CHANGE IN POWER. STRONG WAVE ACTION PRESENT. PF THOUGHT HE COULD DO BETTER AND WENT TO MANUAL AND LOST 300'. RETURNED TO ASSIGNED ALT.
Narrative: DURING CRUISE AT FL370 IN MLG WITH PMS CTLING THE AUTOTHROTTLES, WE ENCOUNTERED WAVE ACTION WHICH CAUSED THE THROTTLES TO GO ALL THE WAY FROM 1.22 TO 2.03 EPR. I THOUGHT I COULD MAKE A BETTER RIDE W/O THE LARGE PWR CHANGES BEING MADE BY PMS SO I TURNED THE AUTOTHROTTLES OFF AND REDUCED THE EPR TO 1.8. AFTER CHKING SPD TO MAKE SURE IT DIDN'T BLEED OFF I NOTICED THE PITCH WINDOW OF THE FMA WAS READING MACH INSTEAD OF ALT HOLD. AS I REACHED TO TOUCH THE ALT HOLD BUTTON THE ALT ALERT WARNED 'ALT.' I DISCONNECTED THE AUTOPLT ADDED PWR AND GOT RIGHT SMARTLY BACK TO FL370 FROM FL367. AS WE APCHED FL370 WITHIN 50' THE CTLR ASKED US TO CONFIRM WE WERE AT FL370 WHICH WE DID SINCE WE WERE THERE AGAIN. I'M SURE HIS SWITCH WENT OFF SINCE WE WERE WITHIN 2-3 MI OF XING TFC AT FL350. HUMAN PERFORMANCE CONSIDERATIONS: ALTHOUGH THE TRNING AT MY CARRIER IS EXCELLENT I FEEL I WAS LET DOWN HERE. A BOOK ON PMS AND SOME DISCUSSION OF PMS ON MY LOG DIDN'T CUT IT. I ALSO FEEL THIS IS A DESIGN FLAW. TURNING AUTOTHROTTLES OFF SHOULD NOT CAUSE YOU TO LOSE THE ALT HOLD FUNCTION. INSTEAD OF FAILING FROM PERFORMANCE CRUISE TO MACH IT SHOULD FAIL FROM PERFORMANCE CRUISE TO ALT HOLD. NEW GENERATION ELECTRONICS ARE WONDERFUL BUT THE MONITORING WORKLOAD IS CONSIDERABLE AND I HATE FINDING THE BUILT IN TRAPS THIS WAY.
Data retrieved from NASA's ASRS site as of August 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.