Narrative:

Dispatched with an intermix of 22000 and 20000 pounds of thrust engines. The bulletin states 'there may also be a placard on the forward panel below the engine instruments indicating which type engine is in each location.' the intermix was indicated by a placard above each set of engine instruments. Apparently, the placards are not required and the location of the placard is optional. Although the bulletin states 'available thrust of both engines will be identical', it was not so! On takeoff and during climb throttle stagger exceeded 2 knob widths. After takeoff I disconnected the autothrottles. I was able to obtain significantly more RPM from the 22000 pounds of thrust engine. If my memory is correct, the rule of thumb is 'thrust varies with the cube of the RPM.' therefore, we could have pushed the throttles full forward and operate with asymmetrical thrust. In the event of an engine failure and application of full forward throttle, we would have been operating a B2 (22000) with B1 (20000) flight data. There is a significant difference between the vmcg speed between B1 and B2 pwred aircraft. The takeoff/landing data card was for a B1 pwred aircraft. At low takeoff gross weights with an engine failure of the B1 engine, we could have been outside the operating envelope for the actual engine confign of the aircraft. Is the bulletin inaccurate? Did maintenance not perform the required procedures to ensure that the asymmetrical thrust situation could not occur. Are the maintenance procedures inadequate? Otherwise how could we have ended up with more than 2 knob widths of throttle stagger? Does the maintenance procedure require a full power runup? If so, why wasn't it accomplished. If the maintenance procedures do not require a full power runup, why not? Callback conversation with reporter revealed the following information: reporter was unable to add anything to his report. He has many questions and none of them have been answered. Therefore, he was unable to answer analyst's questions. He wondered aloud if: if full power was available to the pilot, what would the vmcg be and how would the flight crew determine the vmcg which would depend on which engine failed. He is very critical of the MEL system. He said aircraft was grounded on arrival at bdl.

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Original NASA ASRS Text

Title: RPTR COMPLAINS ABOUT ACFT ON LINE WITH 2 DIFFERENT TYPES OF ENGS, 1 10 PERCENT MORE PWRFUL THAN THE OTHER, THAT COULD CREATE 'VMCG' PROBLEMS IF 1 ENG QUIT AT LOW AIRSPDS.

Narrative: DISPATCHED WITH AN INTERMIX OF 22000 AND 20000 POUNDS OF THRUST ENGS. THE BULLETIN STATES 'THERE MAY ALSO BE A PLACARD ON THE FORWARD PANEL BELOW THE ENG INSTS INDICATING WHICH TYPE ENG IS IN EACH LOCATION.' THE INTERMIX WAS INDICATED BY A PLACARD ABOVE EACH SET OF ENG INSTS. APPARENTLY, THE PLACARDS ARE NOT REQUIRED AND THE LOCATION OF THE PLACARD IS OPTIONAL. ALTHOUGH THE BULLETIN STATES 'AVAILABLE THRUST OF BOTH ENGS WILL BE IDENTICAL', IT WAS NOT SO! ON TKOF AND DURING CLB THROTTLE STAGGER EXCEEDED 2 KNOB WIDTHS. AFTER TKOF I DISCONNECTED THE AUTOTHROTTLES. I WAS ABLE TO OBTAIN SIGNIFICANTLY MORE RPM FROM THE 22000 POUNDS OF THRUST ENG. IF MY MEMORY IS CORRECT, THE RULE OF THUMB IS 'THRUST VARIES WITH THE CUBE OF THE RPM.' THEREFORE, WE COULD HAVE PUSHED THE THROTTLES FULL FORWARD AND OPERATE WITH ASYMMETRICAL THRUST. IN THE EVENT OF AN ENG FAILURE AND APPLICATION OF FULL FORWARD THROTTLE, WE WOULD HAVE BEEN OPERATING A B2 (22000) WITH B1 (20000) FLT DATA. THERE IS A SIGNIFICANT DIFFERENCE BTWN THE VMCG SPD BTWN B1 AND B2 PWRED ACFT. THE TKOF/LNDG DATA CARD WAS FOR A B1 PWRED ACFT. AT LOW TKOF GROSS WTS WITH AN ENG FAILURE OF THE B1 ENG, WE COULD HAVE BEEN OUTSIDE THE OPERATING ENVELOPE FOR THE ACTUAL ENG CONFIGN OF THE ACFT. IS THE BULLETIN INACCURATE? DID MAINT NOT PERFORM THE REQUIRED PROCS TO ENSURE THAT THE ASYMMETRICAL THRUST SITUATION COULD NOT OCCUR. ARE THE MAINT PROCS INADEQUATE? OTHERWISE HOW COULD WE HAVE ENDED UP WITH MORE THAN 2 KNOB WIDTHS OF THROTTLE STAGGER? DOES THE MAINT PROC REQUIRE A FULL PWR RUNUP? IF SO, WHY WASN'T IT ACCOMPLISHED. IF THE MAINT PROCS DO NOT REQUIRE A FULL PWR RUNUP, WHY NOT? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS UNABLE TO ADD ANYTHING TO HIS RPT. HE HAS MANY QUESTIONS AND NONE OF THEM HAVE BEEN ANSWERED. THEREFORE, HE WAS UNABLE TO ANSWER ANALYST'S QUESTIONS. HE WONDERED ALOUD IF: IF FULL PWR WAS AVAILABLE TO THE PLT, WHAT WOULD THE VMCG BE AND HOW WOULD THE FLC DETERMINE THE VMCG WHICH WOULD DEPEND ON WHICH ENG FAILED. HE IS VERY CRITICAL OF THE MEL SYS. HE SAID ACFT WAS GNDED ON ARR AT BDL.

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.