DA42 WAS REPEATEDLY OPERATED FOR FLT INSTRUCTION WITH A DEICING BOOT MISSING FROM A PROPELLER.

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I FLEW AND PROVIDED FLT INSTRUCTION IN AN UNAIRWORTHY ACFT. THE ACFT IS A DA-41; DIAMOND TWINSTAR 2.0; WITH A MISSING R PROP DEICE BOOT. IT WAS DISCOVERED THAT A DEICE BOOT WAS MISSING FROM THE R PROP. THE AIRPLANE WAS GNDED AND SENT TO MAINT; WHERE THEY GLUED ANOTHER BOOT ONTO THE PROP. 3 DAYS LATER; I WAS FLYING THE AIRPLANE WHEN THE NEWLY ATTACHED BOOT DEPARTED THE AIRPLANE INFLT. EVIDENTLY THERE WAS A TIME REQUIREMENT FOR ALLOWING THE NEWLY GLUED BOOT TO DRY; AND I WAS NOT INFORMED THAT THE BOOT WOULD TAKE AT LEAST 48 HRS TO DRY. NO UNUSUAL VIBRATIONS OR NOISES WERE NOTICED ON THE RETURN FLT. UPON LNDG AND SECURING THE ACFT; I CONTACTED THE CHIEF FLT INSTRUCTOR TO INFORM HIM OF THE PROB. HE INFORMED ME THAT HE BELIEVED THE ACFT WAS STILL AIRWORTHY; AS LONG AS I DIDN'T NOTICE ANY ISSUES WITH VIBRATION. I INFORMED HIM I DID NOT DETECT ANY SUCH ISSUES AND; THEREFORE; I FILLED OUT AN OPEN SQUAWK SHEET; RENDERING THE ACFT AIRWORTHY BY DEFERRING THE MAINT ISSUE; HOWEVER; EFFECTIVELY GNDING THE AIRPLANE FOR FLT INTO IMC AND/OR KNOWN OR FORECAST ICING CONDITIONS. I CONTINUED TO OPERATE THE ACFT VFR WITHIN 50 NM FOR FLT TRAINING PURPOSES; AS DID OTHER FLT INSTRUCTORS I WORK WITH AS WELL AS A DESIGNATED PLT EXAMINER; WHO CONDUCTED A CHK RIDE IN THE ACFT. DURING THE 16 DAYS I FLEW THE ACFT; I NEVER NOTICED ANY VIBRATION ISSUES; NEITHER DID ANY OF THE OTHER INSTRUCTORS WHO FLEW THE ACFT. THE ACFT WAS GNDED; UPON THE SUGGESTION THAT THE ACFT MIGHT NOT BE AIRWORTHY DURING AN INTERVIEW FOR A NEW CHIEF FLT INSTRUCTOR. UPON CONSULTATION OF THE TYPE CERTIFICATE FOR THE ACFT; IT WAS DETERMINED THE ACFT WAS NO LONGER AIRWORTHY; AS IT DID NOT MEET THE SPECS OF ITS ORIGINAL TYPE DESIGN. MY REASONING FOR DEFERRING THIS AS A MAINT ISSUE WAS BASED LARGELY UPON THE ADVICE OF MY IMMEDIATE SUPERIOR; THE CHIEF FLT INSTRUCTOR. IT WAS UPON HIS RECOMMENDATION THAT I CONTINUED TO FLY THE ACFT; EVEN THOUGH IT WAS TECHNICALLY UNAIRWORTHY. AT THE TIME; THERE WERE MANY BACK-TO-BACK FLTS IN THE ACFT; AND THE AMOUNT OF TIME REQUIRED TO LET THE BOOT DRY WOULD HAVE MEANT GNDING THE ACFT FOR 48-72 HRS. OF COURSE; SAFETY WAS ALWAYS PARAMOUNT; HOWEVER; SINCE THE ACFT WAS BELIEVED TO BE AIRWORTHY; NO RUSH WAS MADE TO GND THE ACFT FOR 2 DAYS TO DO THE REPAIR. I RECOGNIZE NOW THAT THE DECISION TO KEEP THE AIRPLANE IN SVC WAS NOT ACCORDING TO 91.213; AND I AM SUBMITTING THIS RPT ON THE BASIS OF MY UNDERSTANDING THAT I DISCOVERED AFTER THE FACT THAT I FLEW AN UNAIRWORTHY ACFT FOR 16 DAYS. SINCE I BELIEVED THE ACFT WAS AIRWORTHY; I AM JUST AS MUCH TO BLAME AS ANYONE ELSE BECAUSE I FAILED TO CHK THE TYPE CERTIFICATE AS REQUIRED BY THE REGS AND RELIED UPON A VERBAL JUSTIFICATION FROM MY CHIEF FLT INSTRUCTOR INSTEAD OF CHKING MYSELF. THE ACFT HAS SINCE BEEN GNDED AND REPAIRED. I BELIEVE THIS INCIDENT AROSE NOT BECAUSE OF NEGLECT; BUT BECAUSE OF LACK OF A DEDICATED MAINT PERSON AND OVERSIGHT INTO THE PROCS FOR OPEN SQUAWKS. I FEEL I HAVE BEEN EDUCATED BY THIS EXPERIENCE AND NOW HAVE A BETTER UNDERSTANDING OF 91.213. I WAS QUICK TO ASSUME THAT 91.205 COVERED ME; WHEN IN FACT I SHOULD HAVE READ 91.213 MORE CAREFULLY.