Narrative:

I have been well aware since I started flying a socata TBM700 pressurized turboprop more than 2 yrs ago that mode C encoded altitude replies drop off air traffic radar screens during climbs and dscnts. This is because the 'model' in the ATC computer does not expect a climb or descend at the rate easily accomplished by a TBM700. Apparently the model is based upon socata non-pressurized piston aircraft. When the computer sees a target outstripping what it thinks should be the plane's performance, it deletes the altitude, assuming the information is erroneous. This often makes for ATC problems, delays handoffs, causes unnecessary leveloffs, and may contribute to traffic conflicts. Of course, it adds to frequency congestion each time a controller and pilot have to confirm the altitude. This happens frequently, and has been noted by a number of TBM700 operators. I consider this a safety hazard. Unfortunately, the ATC handbook and ATC computer simulation of performance are often in error, for many aircraft, and perhaps this is the basis of the computer models. The TBM700 is listed as having a 1700 FPM climb and a 1500 FPM descent in the air traffic control handbook. This is less than a TBM700 typically climbs and descends, and is much less than maximum performance. Because ATC does not understand we are a turboprop, and can descend at 3000 FPM without difficulty, I am cleared to descend below 10000 ft sometimes 100+ mi short of destinations in new jersey, miami, orlando, raleigh, etc. ATC seems not to realize how much more fuel I am expending with prolonged flight below the flight levels. I am also unnecessarily contributing to low level congestion when I could be kept on high until much closer to my destination. Climb out from metropolitan areas are also often prolonged.

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Original NASA ASRS Text

Title: TBM7 PLT CONCERNED WITH OUTPERFORMING THE FAA'S PUBLISHED CLB AND DSCNT PERFORMANCE CERTIFICATION CATEGORIES, CAUSING ADDITIONAL PLT CTLR PERFORMANCE VERIFICATION.

Narrative: I HAVE BEEN WELL AWARE SINCE I STARTED FLYING A SOCATA TBM700 PRESSURIZED TURBOPROP MORE THAN 2 YRS AGO THAT MODE C ENCODED ALT REPLIES DROP OFF AIR TFC RADAR SCREENS DURING CLBS AND DSCNTS. THIS IS BECAUSE THE 'MODEL' IN THE ATC COMPUTER DOES NOT EXPECT A CLB OR DSND AT THE RATE EASILY ACCOMPLISHED BY A TBM700. APPARENTLY THE MODEL IS BASED UPON SOCATA NON-PRESSURIZED PISTON ACFT. WHEN THE COMPUTER SEES A TARGET OUTSTRIPPING WHAT IT THINKS SHOULD BE THE PLANE'S PERFORMANCE, IT DELETES THE ALT, ASSUMING THE INFO IS ERRONEOUS. THIS OFTEN MAKES FOR ATC PROBS, DELAYS HDOFS, CAUSES UNNECESSARY LEVELOFFS, AND MAY CONTRIBUTE TO TFC CONFLICTS. OF COURSE, IT ADDS TO FREQ CONGESTION EACH TIME A CTLR AND PLT HAVE TO CONFIRM THE ALT. THIS HAPPENS FREQUENTLY, AND HAS BEEN NOTED BY A NUMBER OF TBM700 OPERATORS. I CONSIDER THIS A SAFETY HAZARD. UNFORTUNATELY, THE ATC HANDBOOK AND ATC COMPUTER SIMULATION OF PERFORMANCE ARE OFTEN IN ERROR, FOR MANY ACFT, AND PERHAPS THIS IS THE BASIS OF THE COMPUTER MODELS. THE TBM700 IS LISTED AS HAVING A 1700 FPM CLB AND A 1500 FPM DSCNT IN THE AIR TFC CTL HANDBOOK. THIS IS LESS THAN A TBM700 TYPICALLY CLBS AND DSNDS, AND IS MUCH LESS THAN MAX PERFORMANCE. BECAUSE ATC DOES NOT UNDERSTAND WE ARE A TURBOPROP, AND CAN DSND AT 3000 FPM WITHOUT DIFFICULTY, I AM CLRED TO DSND BELOW 10000 FT SOMETIMES 100+ MI SHORT OF DESTS IN NEW JERSEY, MIAMI, ORLANDO, RALEIGH, ETC. ATC SEEMS NOT TO REALIZE HOW MUCH MORE FUEL I AM EXPENDING WITH PROLONGED FLT BELOW THE FLT LEVELS. I AM ALSO UNNECESSARILY CONTRIBUTING TO LOW LEVEL CONGESTION WHEN I COULD BE KEPT ON HIGH UNTIL MUCH CLOSER TO MY DEST. CLB OUT FROM METROPOLITAN AREAS ARE ALSO OFTEN PROLONGED.

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.