Narrative:

I was assigned a crj-900 aircraft to research; clear; or defer an anti-ice fault status message that was a pilot log page write-up. I checked the maintenance diagnostic computer (mdc) and had a fault code message 'left ob wing T snsr' failed/wiring. I was advised by my lead that the aircraft had history and to defer the left outboard temperature sensor. At that time I told the lead that I did not know if it was deferrable and that I hadn't had a chance to look in the MEL book. Maintenance control came on frequency and said that MEL 30-12-4-3 was the one to use. I replied that I was looking at the MEL now and would get back after reading it. The MEL looked good; so I used it but I must admit that it; as well as other MEL's in the crj-900 MEL book can be misleading; confusing; or just difficult to decipher. As a line technician; I feel that I don't need the added burden of trying to 'make a decision' that can affect flight safety with an MEL book that is known to be difficult at best to use at times. This particular MEL lists quantity installed (4); quantity required (2) and lists in remarks and exceptions 'elements' per sensor pair may be inoperative. That's the 'gotcha' that was bugging me at the time. I think at the time we were all focused on the fact that there were two good working elements on a sensor. Just before I released the aircraft; I called on the telephone; the maintenance controller working the flight and wanted to verify if indeed this was going to be a good MEL to use. I received the 'yes' it's good. Feeling that I did everything right; I released and got the maintenance controller's number.I just had that feeling throughout the next hour that the MEL was misleading and immediately talked with the line dayshift supervisor. We again re-read the MEL and he thought it looked good. Now that's three people reading the same deferral agreeing that it was ok. Still not happy; I got the system description manual out and looked at the schematic of the temperature sensors. At this point we were also in a conference call with the maintenance controller supervisor and the quantity installed versus quantity required came up. Now there are four people thinking the deferral was good. Finally; as I was looking at the sensor wiring; it became apparent that you cannot have a sensor with both channels (mdc reported that channels a and B failed); inoperative on one wing. It can only be one channel (or element) inoperative on either the left or right wing temperature sensors. There's your quantity (2) required. I told the maintenance controller supervisor to ground the aircraft in ZZZ. He did and updated the MEL to 30-12-4-1.the MEL book on the crj-900 can be very difficult to understand; [which] adds an extra burden to an already stressful job of deferring an aircraft system. (My flight in question had a 30-minute turn time and I was being interrupted numerous times by the gate agent and captain with other problems). If four people are reading the same MEL and agreeing that it's good; I think one can see the problem. This is a bad MEL when it comes to temperature sensors. I feel if the MEL was more descriptive; such as; (2) O/B (outboard) temperature sensors installed with (2) elements each; for a total of (4) installed. Two elements are required; but must have at least one operational [channel] on each sensor. I know that from this point of my career; if I defer a system and have that 'inner voice' tugging at my arm; the logbook gets shut and I bring it to the gate shack and sit down for an open discussion on just what the meaning of this deferral is.get all involved to get the aircraft grounded and re-deferred. [Also] suggest getting the necessary changes made to the 'bad' (misleading) mels in the -900 MEL book.

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Original NASA ASRS Text

Title: A Line Mechanic reports confusion surrounding the technical interpretation of their MEL Chapter 30-12-4 requirements when trying to defer wing temperature sensors. Mechanic notes the CRJ-900 Manual can be misleading; confusing and difficult to decipher. Aircraft was released; but immediately grounded at the next station.

Narrative: I was assigned a CRJ-900 aircraft to research; clear; or defer an anti-ice fault status message that was a pilot log page write-up. I checked the Maintenance Diagnostic Computer (MDC) and had a fault code message 'L OB WING T SNSR' failed/wiring. I was advised by my lead that the aircraft had history and to defer the left outboard temperature sensor. At that time I told the lead that I did not know if it was deferrable and that I hadn't had a chance to look in the MEL book. Maintenance Control came on frequency and said that MEL 30-12-4-3 was the one to use. I replied that I was looking at the MEL now and would get back after reading it. The MEL looked good; so I used it but I must admit that it; as well as other MEL's in the CRJ-900 MEL book can be misleading; confusing; or just difficult to decipher. As a Line Technician; I feel that I don't need the added burden of trying to 'make a decision' that can affect flight safety with an MEL book that is known to be difficult at best to use at times. This particular MEL lists quantity installed (4); quantity required (2) and lists in remarks and exceptions 'elements' per sensor pair may be inoperative. That's the 'gotcha' that was bugging me at the time. I think at the time we were all focused on the fact that there were two good working elements on a sensor. Just before I released the aircraft; I called on the telephone; the Maintenance Controller working the flight and wanted to verify if indeed this was going to be a good MEL to use. I received the 'Yes' it's good. Feeling that I did everything right; I released and got the Maintenance Controller's number.I just had that feeling throughout the next hour that the MEL was misleading and immediately talked with the Line Dayshift Supervisor. We again re-read the MEL and he thought it looked good. Now that's three people reading the same deferral agreeing that it was OK. Still not happy; I got the System Description Manual out and looked at the schematic of the temperature sensors. At this point we were also in a conference call with the Maintenance Controller Supervisor and the quantity installed versus quantity required came up. Now there are four people thinking the deferral was good. Finally; as I was looking at the sensor wiring; it became apparent that you cannot have a sensor with both channels (MDC reported that Channels A and B failed); inoperative on one wing. It can only be one channel (or element) inoperative on either the left or right wing temperature sensors. There's your quantity (2) required. I told the Maintenance Controller Supervisor to ground the aircraft in ZZZ. He did and updated the MEL to 30-12-4-1.The MEL book on the CRJ-900 can be very difficult to understand; [which] adds an extra burden to an already stressful job of deferring an aircraft system. (My flight in question had a 30-minute turn time and I was being interrupted numerous times by the Gate Agent and Captain with other problems). If four people are reading the same MEL and agreeing that it's good; I think one can see the problem. This is a bad MEL when it comes to temperature sensors. I feel if the MEL was more descriptive; such as; (2) O/B (outboard) temperature sensors installed with (2) elements each; for a total of (4) installed. Two elements are required; but must have at least one operational [channel] on each sensor. I know that from this point of my career; if I defer a system and have that 'inner voice' tugging at my arm; the logbook gets shut and I bring it to the gate shack and sit down for an open discussion on just what the meaning of this deferral is.Get all involved to get the aircraft grounded and re-deferred. [Also] suggest getting the necessary changes made to the 'bad' (misleading) MELs in the -900 MEL book.

Data retrieved from NASA's ASRS site as of April 2012 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.