The long 19 month grounding of the 737MAX is over. It’s been a long haul but the FAA and EASA released Airworthiness Directive AD 2020-24-02 (AD) on Nov 18 that allows the return of the Boeing 737 MAX to service. It applies to all Boeing 737-8 and 737-9 (737 MAX) airplanes.
These AD's will impact approx. 450 domestic 737MAX's and an equal number in non US airlines. Not to mention Boeings order book! This will be a big boost to Boeing and the industry as a whole as the US and world struggle to recover from the pandemic.
The AD’s require several elements to be put in place:
- Software updates to the Flight Control Computer (FCC) and revisions to the existing Airplane Flight Manual (AFM) to incorporate new and revised flight crew procedures
- Installing new MAX display system (MDS) software
- Software updates to the Maneuvering Characteristic Augmentation System (MCAS)
- A mandatory pilot training program including simulator training
- Rewiring : although this was not directly related to the accidents, the in depth review showed a need to separate and reroute wires from the flight deck to the stabilizer trim motor in order to comply with FAA wire separation requirements (14CFR 25.1707)
- Completion of an angle of attack (AOA) sensor system test
- Performing an operational readiness flight.
Impact on the Airlines
Flight crew training will need 3 hr. of classroom/computer training and briefings plus ~2hrs of simulator training. However the number of eligible pilots and the availability of simulators may impact this.
Equipment wise: the 385 aircraft in long-term storage will each take ~300 hr. to “de-preserve” plus ~400 hours for software and wiring modifications ~30 days. For the ~450 undelivered aircraft, Boeing estimates that it’ll take 384 hours (16 days) to reactivate/prep the engines, install software updates, testing and a test flight and for customer inspections and certifications.
Wiring Protection -DTI’s specialty- Is Critical.
A worrying finding made by the FAA is that the 737MAX wiring did not meet certification standards despite the multiple zonal inspections these working aircraft had likely passed.
This explains the required rewiring as the integrity of the EWIS has a significant impact on safe flight – wiring abrasion can lead to data loss, arcing, sparking and fire any of which could be as catastrophic as the MCAS/AOA failure.
DTi Makes the Rewiring Simpler, Faster and At a Lower Cost
The work required involves unbundling wires at specific points and rerouting from the flight deck to the stabilizer trim motor. This work could be complicated due to limited ease of access to some of the compartments.
The work is significant. The FAA estimates that it will take at least 80 hours per plane to make the wire modifications. American Airlines have reported it has taken around 72 hours per aircraft- so broadly in line with the FAA. Anything that makes it easier and simpler could help in terms of cost, efficiency and delivery.
Wire protection has normally been accomplished by applying a nylon grommet per MS21266 with glue. This is a long slow multi step process that can be exceedingly challenging especially in this case if techs are faced with tight hard to access compartments where they need to install or replace grommet edging. DTi has a high performance grommet Spring-Fast® M22529/2 which bypasses many of these issues.
Spring-Fast M22529/2 Core Benefits
- High performance grommet edging -strong retention without adhesives
- Simple finger pressure application – it can be done by feel if access is really tight.
- No adhesives or solvents
- No fixturing
- Saves at least 49% of install costs by significantly reducing touch labor time.
The savings will likely to be greater as the 49% is based on sub assembly production line construction with easy access vs. the finished aircraft with hard to access compartments.
- A steel core that is 100% TPE encapsulated
- A sacrificial cushion for superior abrasion protection.
- The inward leaning castles grip the edge for retention – tested to 20/20/20Gs
- Conformable to holes, edges, long runs, short runs and small radii internal and external corners.
- Best in class performance -proven in military and commercial aerospace for over 35 years.
DTi also offers Protect-Fast braided wrap which is a fast and easy way to further help shield and protect wiring and can provide wire/cable separation.