Narrative:

We had a bird strike on final approach into ZZZ. The bird impacted the left alpha vane and broke the entire vane off of the aircraft. The aircraft was landed without incident. Maintenance was called at ZZZ and fortunately we had 2 company maintenance personnel in ZZZ at the time. Talking with dispatch and the maintenance supervisor; it was decided to MEL the item and send us on to ZZZ1. The MEL for a missing alpha vane is MEL X. All maintenance functions associated with MEL X were completed by our maintenance personnel including other MEL's referred to in MEL X. These other MEL's were for disconnecting the #1 stall warning system via circuit breaker and placarding the autoplt and automatic slat system (single channel). In addition; we talked to maintenance about the possibility of arcing when the heat was turned on to the missing alpha vane. Talking to the maintenance supervisor; it was decided to pull and collar the left alpha vane heat circuit breaker and annotate it in the logbook under the MEL X write-up. We obtained an amended dispatch release for the MEL's and proceeded to our destination. Just prior to descent; we received an ACARS call from dispatch asking if we had MEL Y annotated in our logbook. We quickly looked it up in the MEL and discovered MEL Y related to pitot and angle of attack heat being inoperative. As this was not the case; we sent an ACARS message saying we were operating under MEL X; not MEL Y and let them know that all of our pitot/angle of attack heat was working (with the exception of the missing alpha vane). Dispatch sent us a 'thank you' reply. A couple of mins later; dispatch sent another message asking for voice contact. The captain talked to them. They said they wanted us to divert to ZZZ2 because ZZZ1 had icing and we weren't allowed to fly into it without pitot/angle of attack heat. We again told them that all of our anti-ice was functioning normally. We verified this with the lack of fault lights for these devices and a load increase when they were turned on. They still wanted us to return so we did without incident. Maintenance fixed our problem as the captain talked to dispatch and maintenance to try to figure out what was going on. I don't have firsthand knowledge of the phone call; but from what I understand; after we were airborne; the maintenance supervisor contacted dispatch and told them we didn't have any operational pitot heat system and that we should be operating under MEL Y which prohibits flight into icing conditions. After dispatch found this out; they talked to several chief pilots and maintenance personnel asking if we should fly into icing conditions under MEL Y. The answer is no. That's when they diverted us. MEL X deals with missing or broken alpha vanes. Nowhere within this MEL or its associated MEL's does flight in icing even get mentioned. It certainly doesn't prohibit flight into it. MEL Y deals with an inoperable alpha vane heater. This MEL does prohibit flight into icing conditions; but it's my opinion that this MEL doesn't apply to a broken vane. If it did; it would be in the associated MEL's under MEL X. I think the difference between the two is that under MEL X; the broken vane's inputs to the stall computers are removed via the stall warning circuit breaker being pulled (part of the MEL X procedure). It can't give any erroneous signals in or out of icing. In MEL Y; the vane is still sending signals but will be sending incorrect signals should the vane ice up. This could cause a stall warning when no stall conditions exist; or worse; it could cause the lack of a stall warning when one is imminent. The only way I can think of to keep this from happening again is to add a statement to MEL X that states 'flight into icing conditions is permitted.' I firmly believe that the problem was initially analyzed correctly by the ZZZ maintenance personnel; crew; dispatch; and maintenance supervisor in our headquarters city while the plane was on the ground in ZZZ. The correct MEL for this incident is MEL X (missing alpha vane); which is what we were operating under. I don't know how MEL Y got brought up but in my opinion; I don't think it applies. All heat was working properly; verified by the absence of fault lights; load increase when the switch was turned on; and by me touching the warm pitot tubes when we pulled in to the gate. The only heat not working was to the alpha vane that had broken off and been deferred under MEL X. Communication confusion over MEL procedures. Supplemental information from acn 773288: arriving ZZZ on first leg of pairing; we hit a bird that removed the left angle of attack vane. We had 2 mechanics on the field who were awaiting parts for another plane. They did the bird strike inspection and began the MEL procedures with maintenance control. It was properly determined to use MEL X. All provisos were complied with and properly placarded. I conferred with one of the mechanics about my concern with sending power to a non existent angle of attack vane. I felt there may be a problem with arcing; sparking or a short. We agreed that pulling and collaring the left angle of attack heat circuit breaker was the prudent thing to do; which we did. This mechanic then called maintenance control to see if a new log entry needed to be made. He was told to just make a note on the original discrepancy page about pulling and collaring the left angle of attack vane circuit breaker; which was done. Confident that we had done everything properly; we launched for our destination. At cruise we got an ACARS from dispatch asking if we were operating under MEL Y; to which we replied negative; we were under MEL X as he had dispatched us. We later get a call for voice contact which covered the same data: missing angle of attack vane; pulled/collared angle of attack heat circuit breaker. As we began our initial descent; we get another voice call from dispatch directing us to take the plane to ZZZ2 to have the angle of attack vane replaced; saying they now felt we were under MEL Y; which prohibits operating in icing conditions; which MEL X does not contain this prohibition. We reluctantly complied with the directive to take the plane to ZZZ2; had the angle of attack vane replaced; and departed for ZZZ1. I had an extensive conversation with my dispatcher and his supervisor about how this event had unfolded. They explained to me that after extensive discussions with maintenance control; chief pilots; and even the vice president of flight operations; that the right thing to do was to bring the plane to ZZZ2. I am totally convinced that we were operating under the proper MEL (X) for what we had; and there is no prohibition for operating in icing. MEL X needs an additional provision to prohibit operating in icing conditions. Callback conversation with reporter acn 773295 revealed the following information: reporter stated all he wanted was to get some consistency between MEL's X and Y regarding the angle of attack (aoa) vane and whether dispatch is allowed into icing conditions. MEL X doesn't have any restrictions for operating in icing conditions with the aoa missing or damaged. Under MEL X; the broken vane's inputs to the stall warning computers are removed via the stall warning circuit breaker being pulled. The question of proper dispatch release and operating the aircraft in icing conditions became an issue after dispatch realized the broken aoa vane's heater circuit breaker was also pulled and collared. This procedure falls under MEL Y; which does not allow for dispatch into icing conditions. Reporter stated language should be added to MEL X that specifically states whether or not the aircraft is allowed to operate in icing condition.

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Original NASA ASRS Text

Title: A B737-300 FLIGHT CREW REPORTS ON THE DEFERRAL OF A BROKEN ANGLE OF ATTACK (AOA) VANE AND THE RESULTANT CONFUSION OF USING ONE MEL VERSUS ANOTHER FOR DISPATCH INTO ICING CONDITIONS.

Narrative: WE HAD A BIRD STRIKE ON FINAL APCH INTO ZZZ. THE BIRD IMPACTED THE L ALPHA VANE AND BROKE THE ENTIRE VANE OFF OF THE ACFT. THE ACFT WAS LANDED WITHOUT INCIDENT. MAINT WAS CALLED AT ZZZ AND FORTUNATELY WE HAD 2 COMPANY MAINT PERSONNEL IN ZZZ AT THE TIME. TALKING WITH DISPATCH AND THE MAINT SUPVR; IT WAS DECIDED TO MEL THE ITEM AND SEND US ON TO ZZZ1. THE MEL FOR A MISSING ALPHA VANE IS MEL X. ALL MAINT FUNCTIONS ASSOCIATED WITH MEL X WERE COMPLETED BY OUR MAINT PERSONNEL INCLUDING OTHER MEL'S REFERRED TO IN MEL X. THESE OTHER MEL'S WERE FOR DISCONNECTING THE #1 STALL WARNING SYS VIA CIRCUIT BREAKER AND PLACARDING THE AUTOPLT AND AUTO SLAT SYS (SINGLE CHANNEL). IN ADDITION; WE TALKED TO MAINT ABOUT THE POSSIBILITY OF ARCING WHEN THE HEAT WAS TURNED ON TO THE MISSING ALPHA VANE. TALKING TO THE MAINT SUPVR; IT WAS DECIDED TO PULL AND COLLAR THE L ALPHA VANE HEAT CIRCUIT BREAKER AND ANNOTATE IT IN THE LOGBOOK UNDER THE MEL X WRITE-UP. WE OBTAINED AN AMENDED DISPATCH RELEASE FOR THE MEL'S AND PROCEEDED TO OUR DEST. JUST PRIOR TO DSCNT; WE RECEIVED AN ACARS CALL FROM DISPATCH ASKING IF WE HAD MEL Y ANNOTATED IN OUR LOGBOOK. WE QUICKLY LOOKED IT UP IN THE MEL AND DISCOVERED MEL Y RELATED TO PITOT AND ANGLE OF ATTACK HEAT BEING INOP. AS THIS WAS NOT THE CASE; WE SENT AN ACARS MESSAGE SAYING WE WERE OPERATING UNDER MEL X; NOT MEL Y AND LET THEM KNOW THAT ALL OF OUR PITOT/ANGLE OF ATTACK HEAT WAS WORKING (WITH THE EXCEPTION OF THE MISSING ALPHA VANE). DISPATCH SENT US A 'THANK YOU' REPLY. A COUPLE OF MINS LATER; DISPATCH SENT ANOTHER MESSAGE ASKING FOR VOICE CONTACT. THE CAPT TALKED TO THEM. THEY SAID THEY WANTED US TO DIVERT TO ZZZ2 BECAUSE ZZZ1 HAD ICING AND WE WEREN'T ALLOWED TO FLY INTO IT WITHOUT PITOT/ANGLE OF ATTACK HEAT. WE AGAIN TOLD THEM THAT ALL OF OUR ANTI-ICE WAS FUNCTIONING NORMALLY. WE VERIFIED THIS WITH THE LACK OF FAULT LIGHTS FOR THESE DEVICES AND A LOAD INCREASE WHEN THEY WERE TURNED ON. THEY STILL WANTED US TO RETURN SO WE DID WITHOUT INCIDENT. MAINT FIXED OUR PROB AS THE CAPT TALKED TO DISPATCH AND MAINT TO TRY TO FIGURE OUT WHAT WAS GOING ON. I DON'T HAVE FIRSTHAND KNOWLEDGE OF THE PHONE CALL; BUT FROM WHAT I UNDERSTAND; AFTER WE WERE AIRBORNE; THE MAINT SUPVR CONTACTED DISPATCH AND TOLD THEM WE DIDN'T HAVE ANY OPERATIONAL PITOT HEAT SYS AND THAT WE SHOULD BE OPERATING UNDER MEL Y WHICH PROHIBITS FLT INTO ICING CONDITIONS. AFTER DISPATCH FOUND THIS OUT; THEY TALKED TO SEVERAL CHIEF PLTS AND MAINT PERSONNEL ASKING IF WE SHOULD FLY INTO ICING CONDITIONS UNDER MEL Y. THE ANSWER IS NO. THAT'S WHEN THEY DIVERTED US. MEL X DEALS WITH MISSING OR BROKEN ALPHA VANES. NOWHERE WITHIN THIS MEL OR ITS ASSOCIATED MEL'S DOES FLT IN ICING EVEN GET MENTIONED. IT CERTAINLY DOESN'T PROHIBIT FLT INTO IT. MEL Y DEALS WITH AN INOPERABLE ALPHA VANE HEATER. THIS MEL DOES PROHIBIT FLT INTO ICING CONDITIONS; BUT IT'S MY OPINION THAT THIS MEL DOESN'T APPLY TO A BROKEN VANE. IF IT DID; IT WOULD BE IN THE ASSOCIATED MEL'S UNDER MEL X. I THINK THE DIFFERENCE BTWN THE TWO IS THAT UNDER MEL X; THE BROKEN VANE'S INPUTS TO THE STALL COMPUTERS ARE REMOVED VIA THE STALL WARNING CIRCUIT BREAKER BEING PULLED (PART OF THE MEL X PROC). IT CAN'T GIVE ANY ERRONEOUS SIGNALS IN OR OUT OF ICING. IN MEL Y; THE VANE IS STILL SENDING SIGNALS BUT WILL BE SENDING INCORRECT SIGNALS SHOULD THE VANE ICE UP. THIS COULD CAUSE A STALL WARNING WHEN NO STALL CONDITIONS EXIST; OR WORSE; IT COULD CAUSE THE LACK OF A STALL WARNING WHEN ONE IS IMMINENT. THE ONLY WAY I CAN THINK OF TO KEEP THIS FROM HAPPENING AGAIN IS TO ADD A STATEMENT TO MEL X THAT STATES 'FLT INTO ICING CONDITIONS IS PERMITTED.' I FIRMLY BELIEVE THAT THE PROB WAS INITIALLY ANALYZED CORRECTLY BY THE ZZZ MAINT PERSONNEL; CREW; DISPATCH; AND MAINT SUPVR IN OUR HEADQUARTERS CITY WHILE THE PLANE WAS ON THE GND IN ZZZ. THE CORRECT MEL FOR THIS INCIDENT IS MEL X (MISSING ALPHA VANE); WHICH IS WHAT WE WERE OPERATING UNDER. I DON'T KNOW HOW MEL Y GOT BROUGHT UP BUT IN MY OPINION; I DON'T THINK IT APPLIES. ALL HEAT WAS WORKING PROPERLY; VERIFIED BY THE ABSENCE OF FAULT LIGHTS; LOAD INCREASE WHEN THE SWITCH WAS TURNED ON; AND BY ME TOUCHING THE WARM PITOT TUBES WHEN WE PULLED IN TO THE GATE. THE ONLY HEAT NOT WORKING WAS TO THE ALPHA VANE THAT HAD BROKEN OFF AND BEEN DEFERRED UNDER MEL X. COM CONFUSION OVER MEL PROCS. SUPPLEMENTAL INFO FROM ACN 773288: ARRIVING ZZZ ON FIRST LEG OF PAIRING; WE HIT A BIRD THAT REMOVED THE L ANGLE OF ATTACK VANE. WE HAD 2 MECHS ON THE FIELD WHO WERE AWAITING PARTS FOR ANOTHER PLANE. THEY DID THE BIRD STRIKE INSPECTION AND BEGAN THE MEL PROCS WITH MAINT CTL. IT WAS PROPERLY DETERMINED TO USE MEL X. ALL PROVISOS WERE COMPLIED WITH AND PROPERLY PLACARDED. I CONFERRED WITH ONE OF THE MECHS ABOUT MY CONCERN WITH SENDING PWR TO A NON EXISTENT ANGLE OF ATTACK VANE. I FELT THERE MAY BE A PROB WITH ARCING; SPARKING OR A SHORT. WE AGREED THAT PULLING AND COLLARING THE L ANGLE OF ATTACK HEAT CIRCUIT BREAKER WAS THE PRUDENT THING TO DO; WHICH WE DID. THIS MECH THEN CALLED MAINT CTL TO SEE IF A NEW LOG ENTRY NEEDED TO BE MADE. HE WAS TOLD TO JUST MAKE A NOTE ON THE ORIGINAL DISCREPANCY PAGE ABOUT PULLING AND COLLARING THE L ANGLE OF ATTACK VANE CIRCUIT BREAKER; WHICH WAS DONE. CONFIDENT THAT WE HAD DONE EVERYTHING PROPERLY; WE LAUNCHED FOR OUR DEST. AT CRUISE WE GOT AN ACARS FROM DISPATCH ASKING IF WE WERE OPERATING UNDER MEL Y; TO WHICH WE REPLIED NEGATIVE; WE WERE UNDER MEL X AS HE HAD DISPATCHED US. WE LATER GET A CALL FOR VOICE CONTACT WHICH COVERED THE SAME DATA: MISSING ANGLE OF ATTACK VANE; PULLED/COLLARED ANGLE OF ATTACK HEAT CIRCUIT BREAKER. AS WE BEGAN OUR INITIAL DSCNT; WE GET ANOTHER VOICE CALL FROM DISPATCH DIRECTING US TO TAKE THE PLANE TO ZZZ2 TO HAVE THE ANGLE OF ATTACK VANE REPLACED; SAYING THEY NOW FELT WE WERE UNDER MEL Y; WHICH PROHIBITS OPERATING IN ICING CONDITIONS; WHICH MEL X DOES NOT CONTAIN THIS PROHIBITION. WE RELUCTANTLY COMPLIED WITH THE DIRECTIVE TO TAKE THE PLANE TO ZZZ2; HAD THE ANGLE OF ATTACK VANE REPLACED; AND DEPARTED FOR ZZZ1. I HAD AN EXTENSIVE CONVERSATION WITH MY DISPATCHER AND HIS SUPVR ABOUT HOW THIS EVENT HAD UNFOLDED. THEY EXPLAINED TO ME THAT AFTER EXTENSIVE DISCUSSIONS WITH MAINT CTL; CHIEF PLTS; AND EVEN THE VICE PRESIDENT OF FLT OPS; THAT THE RIGHT THING TO DO WAS TO BRING THE PLANE TO ZZZ2. I AM TOTALLY CONVINCED THAT WE WERE OPERATING UNDER THE PROPER MEL (X) FOR WHAT WE HAD; AND THERE IS NO PROHIBITION FOR OPERATING IN ICING. MEL X NEEDS AN ADDITIONAL PROVISION TO PROHIBIT OPERATING IN ICING CONDITIONS. CALLBACK CONVERSATION WITH RPTR ACN 773295 REVEALED THE FOLLOWING INFO: REPORTER STATED ALL HE WANTED WAS TO GET SOME CONSISTENCY BETWEEN MEL'S X AND Y REGARDING THE ANGLE OF ATTACK (AOA) VANE AND WHETHER DISPATCH IS ALLOWED INTO ICING CONDITIONS. MEL X DOESN'T HAVE ANY RESTRICTIONS FOR OPERATING IN ICING CONDITIONS WITH THE AOA MISSING OR DAMAGED. UNDER MEL X; THE BROKEN VANE'S INPUTS TO THE STALL WARNING COMPUTERS ARE REMOVED VIA THE STALL WARNING CIRCUIT BREAKER BEING PULLED. THE QUESTION OF PROPER DISPATCH RELEASE AND OPERATING THE ACFT IN ICING CONDITIONS BECAME AN ISSUE AFTER DISPATCH REALIZED THE BROKEN AOA VANE'S HEATER CIRCUIT BREAKER WAS ALSO PULLED AND COLLARED. THIS PROCEDURE FALLS UNDER MEL Y; WHICH DOES NOT ALLOW FOR DISPATCH INTO ICING CONDITIONS. REPORTER STATED LANGUAGE SHOULD BE ADDED TO MEL X THAT SPECIFICALLY STATES WHETHER OR NOT THE ACFT IS ALLOWED TO OPERATE IN ICING CONDITION.

Data retrieved from NASA's ASRS site as of May 2009 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.