Date: 201403
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Night
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Confusion; Communication Breakdown
Second reporter function: Technician
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
Result: General Maintenance Action
Contributing factors: Procedure; Manuals; Human Factors; Chart Or Publication
Primary problem: Manuals

Narrative: On B737 Periodic Service (P/S) Check (and maybe other Job cards); Step 2 (E) tells to check tire Step Wear and lists Figure-1 for explanation. Figure-1 doesn't clearly explain what STEP WEAR actually is.  Note-2 seems to say that only when I see fabric; there is Step Wear; is this correct?  I've always thought when the shoulder side tread wears more quickly than the crown; that is Step Wear.  I; later the next day; had a heated argument with another Mechanic on this; and need final and clear explanation; as one of us is clearly not reading the requirement correctly. Does it mean that the outboard shoulder side of the tread must have 3/32' of an inch of tire tread left; or that either side of the tire groove; crown or shoulder; can have that 3/32' of an inch [remaining] for the tire to be good?[Recommend] our air carrier clearly explain in the PS Check and General Procedures Manual (GPM) if the shoulder side tread requires 3/32' tread or not; and also explain if the tire is serviceable with the shoulder side to be below 3/32' of an inch; if the crown side is still above 3/32' of an inch.


Second narrative: Reference Procedures Manual (PM) 7-02-4. I have recently observed two very heated arguments between mechanics regarding interpretation of Tire Tread Wear limits. The topic has both times been about measuring wear on the outermost tread; the tread between the crown and shoulder. The disputes were whether the crown side and the tread side [of the tire] both require 2/32' of an inch (3/32' for B737) tread [remaining]; or more; to be considered a Serviceable Tire.My understanding is both tread sides require 2/32' of an inch (or 3/32') in order to be Serviceable.  Request answer: Are the shoulder and crown tread sides BOTH expected to be above the 2/32' (3/32') minimum in order for the wear to be serviceable?[Recommend] clarification in the Procedures Manual (PM) what the wear expectation is; as some seem to understand the PM expectation is the shoulder side [of the tire] isn't actually a 'tread' when looking at Figure 7-02-3.  Figure 7-02-2 shows both RIB and TREAD locations. Suggest replace word RIB with TREAD;  Figure  7-02-3 shows word TREAD RIB for inner treads; but nothing for the shoulder tread; suggest adding arrow and identifying SHOULDER TREAD.


Synopsis: Two Aircraft Maintenance Technicians (AMTs) request clarification in their Periodic Service Check and Procedures Manual for measuring Tire Tread Wear Limits on their B737-800 Main Landing Gear (MLG) tires. Also noted were the different interpretations of what STEP WEAR actually was and whether the inboard; outboard; or both shoulder side treads required 3/32 of an inch of tread remaining; for the tire to be considered serviceable.