An air carrier MD80 flight crew find that their performance data for the optimum cruise altitude was in error because they were heavier than the weight and balance totals indicated. Emergency declared.

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Attributes
ACN	432256
Time
Date	199902
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : txk.vortac
State Reference	AR
Altitude	msl single value : 33000
Environment
Weather Elements	Thunderstorm
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	432256
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : multi engine pilot : instrument
ASRS Report	432255
Events
Anomaly	conflict : ground less severe non adherence : far other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	controller : issued advisory controller : issued new clearance flight crew : exited adverse environment
Consequence	other Other
Supplementary
Problem Areas	Company
Primary Problem	Company

Narrative:

While climbing to our cleared altitude of FL330 from FL290, ATC requested we expedite our climb. The required climb rate was 1000 FPM. We leveled off at 240 KIAS, mach .690. While level, the airspeed started to decrease despite maximum continuous thrust being selected on the thrust rating indicator. We immediately requested a descent back to FL290, but was denied by ATC due to conflicting traffic. As the airspeed continued to decrease, we encountered moderate turbulence, and once again asked for an immediate descent and was denied clearance again. At 1-2 KTS below 230 KIAS, a slight buffet developed. We declared an emergency and descended back to FL290 with a 20 degree heading change provided by ATC. Subsequent check of the performance manual revealed the optimum cruise altitude for a 135000 pound aircraft at .76 mach cruise to be a little above FL330, concurring with the pms, initial buffet boundary to be 212 KIAS, and engine holding speed to be 241 KIAS. Weight audit upon landing showed an overage of 31 bags than that accounting for on the closeout.

Original NASA ASRS Text

Title: AN ACR MD80 FLC FIND THAT THEIR PERFORMANCE DATA FOR THE OPTIMUM CRUISE ALT WAS IN ERROR BECAUSE THEY WERE HEAVIER THAN THE WT AND BAL TOTALS INDICATED. EMER DECLARED.

Narrative: WHILE CLBING TO OUR CLRED ALT OF FL330 FROM FL290, ATC REQUESTED WE EXPEDITE OUR CLB. THE REQUIRED CLB RATE WAS 1000 FPM. WE LEVELED OFF AT 240 KIAS, MACH .690. WHILE LEVEL, THE AIRSPD STARTED TO DECREASE DESPITE MAX CONTINUOUS THRUST BEING SELECTED ON THE THRUST RATING INDICATOR. WE IMMEDIATELY REQUESTED A DSCNT BACK TO FL290, BUT WAS DENIED BY ATC DUE TO CONFLICTING TFC. AS THE AIRSPD CONTINUED TO DECREASE, WE ENCOUNTERED MODERATE TURB, AND ONCE AGAIN ASKED FOR AN IMMEDIATE DSCNT AND WAS DENIED CLRNC AGAIN. AT 1-2 KTS BELOW 230 KIAS, A SLIGHT BUFFET DEVELOPED. WE DECLARED AN EMER AND DSNDED BACK TO FL290 WITH A 20 DEG HDG CHANGE PROVIDED BY ATC. SUBSEQUENT CHK OF THE PERFORMANCE MANUAL REVEALED THE OPTIMUM CRUISE ALT FOR A 135000 LB ACFT AT .76 MACH CRUISE TO BE A LITTLE ABOVE FL330, CONCURRING WITH THE PMS, INITIAL BUFFET BOUNDARY TO BE 212 KIAS, AND ENG HOLDING SPD TO BE 241 KIAS. WT AUDIT UPON LNDG SHOWED AN OVERAGE OF 31 BAGS THAN THAT ACCOUNTING FOR ON THE CLOSEOUT.

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.