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An MD80 weighing 137000 pounds attempted to climb to FL340 but had to descend after the aircraft entered a light stall buffet at 200 KTS.
| Attributes | |
| ACN | 798717 |
| Time | |
| Date | 200808 |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | airport : zzz.airport |
| State Reference | US |
| Altitude | msl bound lower : 32000 msl bound upper : 33000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zzz.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | MD-88 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : enroute altitude change |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time total : 17000 |
| ASRS Report | 798717 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 250 flight time total : 5500 flight time type : 600 |
| ASRS Report | 799096 |
| Events | |
| Anomaly | altitude deviation : undershoot altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other anomaly |
| Independent Detector | other flight crewa other flight crewb |
| Resolutory Action | flight crew : exited adverse environment flight crew : regained aircraft control |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance Aircraft |
| Primary Problem | Flight Crew Human Performance |
Narrative:
We departed ZZZ for ZZZ1. It was the captain's leg. The autothrottles were inoperative. We leveled at FL330; near ZZZ2. We checked our weight; 137000 pounds; and changed the speed booklet to that weight. We then bugged 10 KTS. Above clean speed; 250 KTS. Set the throttles to 1.68 EPR. This was holding .75 mach. ATC called and asked if we could accept FL340. We both checked the FMS and verified that we could climb to FL340. The autoplt was on; so we selected 800 FPM and advanced the throttles to climb power. It was at this point that we both noticed that our airspeed was 225 KTS. It stayed at 225 KTS until we reached FL335; even though I had reduced our vertical speed to 300 FPM. At this point the airspeed decayed to 200 KTS; I stopped the climb and requested a descent back down to FL320. ATC said that they couldn't let us descend. Started to feel light buffet. Informed ATC that we were beginning a descent. Shortly thereafter ATC cleared us to descend to FL300. As we descended we were able to accelerate to 260 KTS. ATC made no mention of any kind of conflict with any other aircraft. The event was caused by 2 things. First; the autothrottles were inoperative. Second; I was not in the habit of crosschking airspeed as often as I should have without autothrottles being available (habit pattern). Finally; the company uses a cost index of 11 in the FMS. This keeps the aircraft too close to the bottom margin. Without autothrottles I should have used a higher cost index.
Original NASA ASRS Text
Title: AN MD80 WEIGHING 137000 LBS ATTEMPTED TO CLB TO FL340 BUT HAD TO DSND AFTER THE ACFT ENTERED A LIGHT STALL BUFFET AT 200 KTS.
Narrative: WE DEPARTED ZZZ FOR ZZZ1. IT WAS THE CAPT'S LEG. THE AUTOTHROTTLES WERE INOP. WE LEVELED AT FL330; NEAR ZZZ2. WE CHKED OUR WT; 137000 LBS; AND CHANGED THE SPD BOOKLET TO THAT WT. WE THEN BUGGED 10 KTS. ABOVE CLEAN SPD; 250 KTS. SET THE THROTTLES TO 1.68 EPR. THIS WAS HOLDING .75 MACH. ATC CALLED AND ASKED IF WE COULD ACCEPT FL340. WE BOTH CHKED THE FMS AND VERIFIED THAT WE COULD CLB TO FL340. THE AUTOPLT WAS ON; SO WE SELECTED 800 FPM AND ADVANCED THE THROTTLES TO CLB PWR. IT WAS AT THIS POINT THAT WE BOTH NOTICED THAT OUR AIRSPD WAS 225 KTS. IT STAYED AT 225 KTS UNTIL WE REACHED FL335; EVEN THOUGH I HAD REDUCED OUR VERT SPD TO 300 FPM. AT THIS POINT THE AIRSPD DECAYED TO 200 KTS; I STOPPED THE CLB AND REQUESTED A DSCNT BACK DOWN TO FL320. ATC SAID THAT THEY COULDN'T LET US DSND. STARTED TO FEEL LIGHT BUFFET. INFORMED ATC THAT WE WERE BEGINNING A DSCNT. SHORTLY THEREAFTER ATC CLRED US TO DSND TO FL300. AS WE DSNDED WE WERE ABLE TO ACCELERATE TO 260 KTS. ATC MADE NO MENTION OF ANY KIND OF CONFLICT WITH ANY OTHER ACFT. THE EVENT WAS CAUSED BY 2 THINGS. FIRST; THE AUTOTHROTTLES WERE INOP. SECOND; I WAS NOT IN THE HABIT OF CROSSCHKING AIRSPD AS OFTEN AS I SHOULD HAVE WITHOUT AUTOTHROTTLES BEING AVAILABLE (HABIT PATTERN). FINALLY; THE COMPANY USES A COST INDEX OF 11 IN THE FMS. THIS KEEPS THE ACFT TOO CLOSE TO THE BOTTOM MARGIN. WITHOUT AUTOTHROTTLES I SHOULD HAVE USED A HIGHER COST INDEX.
Data retrieved from NASA's ASRS site as of May 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.