The Boeing 737 AMM Task 71-71-00-200-801-G00 provides instructions for performing an Engine Vents and Drains Inspection. This task outlines the procedure for inspecting all engine vents and drains for leakage. It contains data that helps estimate the condition of a Line Replaceable Unit (LRU) based on the leakage rate observed from the engine vent and drain system.
The leakage rate for different drains is determined under the following conditions:
(1) Operating the engine at minimum idle to monitor fuel or oil leakage from the vents and drains.
(2) Operating the engine at part power to isolate and monitor oil leakage from specific accessory gearbox seals.
Reference Aircraft: Boeing 737 MAX (737-8)
Engine Vents and Drains Leakage Limits
If there are signs of leakage, identify the source of the leak.
FAN DRAIN MAST
- Oil Serviceable limit: 20 cc/hr (7 drops per minute).
- Fuel Serviceable limit: 270 cc/hr (90 drops per minute).
- 25 flight cycles: 180 cc/hr (60 drops per minute) – 270 cc/hr (90 drops per minute)
Fuel Pump Pad Drain
- Leakage from the drain of the Main Fuel Pump can be fuel or oil.
- Oil: Serviceable limit: 20 cc/hr (7 drops per minute).
- Replace the AGB rotating seal – of the applicable pad for the fuel pump, hydraulic pump, hand-cranking pad, or IDG.
- Fuel: Fuel Serviceable limit: 270 cc/hr (90 drops per minute).
- 25 flight cycles: 180 cc/hr (60 drops per minute) – 270 cc/hr (90 drops per minute)
- Replace the main fuel pump.
Service Disconnect (Strut) Drain
- Hydraulic fluid: Serviceable limit: 30 cc/hr (10 drops per minute).
- Fuel: Serviceable limit: 0 cc/hr.
AFT Fairing Drain
- Hydraulic fluid: Serviceable limit: 30 cc/hr (10 drops per minute).
- Fuel: Fuel Serviceable limit: 270 cc/hr (90 drops per minute).
- 25 flight cycles: 180 cc/hr (60 drops per minute) – 270 cc/hr (90 drops per minute)
CORE DRAIN MAST
- If the fuel leakage is less than 180 cc/hr (60 drops per minute), no maintenance action is necessary. If the leakage is more than 180 cc/hr (60 drops per minute) and less than 270 cc/hr (90 drops per minute), you can continue the engine in service for not more than 25 flight cycles before you replace the applicable component.
- Fuel Serviceable limit: 270 cc/hr (90 drops per minute).
- Oil Serviceable limit: 20 cc/hr (7 drops per minute).
The markings on the core drain mast are as follows:
- A-S1: drain line from the A-Sump for the N°1 Roller Bearing
- A-S3: drain line from the A-Sump for the N°3 Roller Bearing
- LRU-L: drain line for the LRUs located on the left-hand side of the engine
- LRU-R: drain line for the LRUs located on the right-hand side of the engine
- AUX: drain line from the TCF
- B-S: drain line from the B-Sump
- C-S: drain line from the C-Sump
20 drops equal to approximately one cc.
For example, 20 drops per minute x 60 = 1200 drops per hour / 20 = 60 cc’s per hour.
