Date: 201809
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Antiskid System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial; Flight Crew Air Transport Pilot (ATP)
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Manuals; Procedure
Primary problem: Aircraft

Narrative: Aircraft was dispatched with MEL 32-XXX; Anti-Skid System. This was the first time either of us had seen this MEL; and since it is fairly extensive; we spent a lot of time briefing it. I felt like we had a good understanding of the requirements and was confident that we could comply. The flight progressed normally until we began configuring for the approach. As we decelerated with the flaps at 15; the First Officer attempted to arm the speed brake lever. Instead of the normal green armed light; we got an amber 'speed brake do not arm light.' The First Officer stowed the handle and tried arming it again; to no avail. I asked him; 'Are we missing something here?.' We had thoroughly briefed the MEL; but we never saw anything that said that we couldn't arm the speed brakes. The MEL states; 'Extend speed brakes manually since automatic extension system MAY not be operative with antiskid inoperative.' We were prepared to manually deploy the speed brakes upon landing; if they didn't automatically deploy. The word 'may' implies that the system might work. How could it possibly work if the speed brake lever is not armed? We thought we had a new problem so we executed a go around to regroup and consult the QRH checklist. The checklist says to land without arming the speed brakes and manually deploy the speed brakes upon landing. We came back around using this procedure and landed without incident. I should add that during our descent; I used the speed brakes and the green armed light came on like it normally does. When we got the do not arm light with flaps extended; it confused me. I thought we had a new problem. Upon arrival at the gate; we contacted Maintenance and they showed me a copy of their 'Speed brake do not arm light is on - fault isolation' troubleshooting procedure (see attached file). This document clearly states that when two anti-skid channels are inoperative (which is what we had); the speed brake do not arm light will come on whenever the speed brake lever is moved to the armed position. In other words; the system is operating normally. At this point; I realized that the intent of the MEL was to NOT arm the speed brake lever; and the manual deploy was required. There is no 'may' or 'might' regarding this. You HAVE to manually deploy the speed brake upon landing. Both my First Officer and I were confused by the word 'may' and the lack of a clear instruction to NOT arm the speed brake lever. Maintenance cleared the logbook and we operated the flight back to ZZZ without further incident.The language in this MEL is confusing and unclear. We made our best effort to comply with the requirements; but we got it wrong.Change the language in the MEL to clearly state that the speed brake lever must not be armed and that manual deployment of the speed brakes are required. Replace the word 'may 'with the word 'will.'One other suggestion from my First Officer [is] a reminder that a bleeds off takeoff may be required would be helpful. We caught it; but it could be easily missed; especially with a 12;000 ft runway in front of you!




Synopsis: B737-800 Captain reported discrepancy between Antiskid MEL crew procedures and QRH crew procedure during approach.