COM PLT COMMENTED ON PROPOSED AIRWORTHINESS DIRECTIVE.

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THIS COMMENT REGARDS THE NOTICE OF PROPOSED RULE MAKING FOR THE AIRWORTHINESS DIRECTIVE ON THE 2-PIECE VENTURI ON OLD (MANUFACTURER'S MODEL) TYPE CARBS AS USED IN THE SMA ACFT. MY SMA ACFT WAS FOUND TO HAVE A DAMAGED PRIMARY VENTURI IN THE CARB DURING ITS ANNUAL INSPECTION IN AUG/84. THE MECH BELIEVED HEAT DAMAGE FROM A BACKFIRE WAS THE CAUSE. THEREFORE; I BELIEVE THAT HIGHER-MELTING-POINT MATERIALS SHOULD BE USED FOR THE PRIMARY VENTURI IN THE MANUFACTURER'S MODEL CARB. THIS VENTURI IS SMALL; FRAGILE; AND EXPOSED TO BACKFIRES. SIMPLY CHANGING THE 2- PIECE CONSTRUCTION TO A 1-PIECE VENTURI MAY BE INADEQUATE. DAMAGE MAY NOT ONLY BE MECHANICAL; BUT MAY ALSO BE DUE TO THERMAL SHOCK. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: A CALLBACK WAS MADE TO THE RPTR TO ADVISE HIM TO MAKE HIS COMMENTS TO THAT ADDRESS SHOWN IN THE PROPOSED 'AIRWORTHINESS DIRECTIVE' AND HE REPLIED THAT HE HAD ALREADY DONE SO AND IN ADDITION DISCUSSED THE MATTER BY TELEPHONE TO THE PERSON RESPONSIBLE FOR COMMENT COLLECTION. HE FURTHER STATED THAT HE HAD SUBMITTED OTHER ASRS RPTS IN THE PAST AND WAS FAVORABLY IMPRESSED WITH THE ASRS WORK AND WANTED US TO KNOW THAT WE DID A GOOD JOB.