Preventive Maintenance for Thrust Reversers
Rugged and reliable, few mechanics consider thrust reversers as a threat to the aircraft's safety. For the airlines, however, they can be a threat to other valuable resources: time and money. Preventable reverser problems can delay flights and, when the problem is significant, force cancellations.
To avoid these problems, and save the carriers needless expense, OEMs stress the need for regular, preventative thrust reverser maintenance. Too many airlines fly reversers Ôon-condition' — meaning little or no attention is given to them until a serious problem occurs.
"It's really no different than your own car," says John Timko, a product support engineer for Middle River Aircraft Systems. "You can never eliminate the chance of getting a flat tire, but if you rotate your tires when you should, keep them properly inflated, and follow the manufacturer's guidelines, then you can greatly reduce the chances that they will leave you stranded."
Timko works directly with the mechanics that service his company's reversers. In addition to the largely composite reverser for the PW4168 engine, Middle River Aircraft Systems (MRAS) is the sole-source supplier of reversers on GE's entire line of CF6 engines. Additionally, the company runs a complete reverser overhaul and repair facility. Everyday, Timko takes calls from mechanics and engineers with questions about reverser's maintenance and performance.
Like most other product support engineers, Timko represents the most direct link to up-to-the-minute, first-hand information about servicing and repairing thrust reversers. Support engineers are most frequently asked about repairs, processes, and general information, or even if a repair or replacement is really necessary. Sometimes a call can save time and money.
Timko remembers a call from a mechanic who noticed cracks along the outside of the transcowl. "It looked like it could be serious, but when he described it, I noticed that it was just the paint cracking in a hidden seam where the transcowl is jointed to the outer surface. Fortunately, this was just a cosmetic problem and was no real threat to the unit."
Clearly the best tool in preventive maintenance is information. Most fleet libraries keep updated Aircraft Maintenance Manuals (AMM) and Component Maintenance Manuals. In addition mechanics should be on the distribution list for the manufacturer's service bulletins and Commercial Engine Service Memorandums (CESM). CESMs and service bulletins are distributed as needed and are the best vehicle for communicating directly with mechanics and service providers. These bulletins may contain information updates on anything from inspection changes to new spare parts.
Like many OEMs, MRAS is working to discourage fleets from flying reversers on-condition. "Planning is the key to saving," says P.K. Bhutiani, vice president of engineering at MRAS. Bhutiani says he understands the time and money constraints that airlines are under, but believes that an on-condition maintenance program is counterproductive.
"Maintenance doesn't cause delays and cancellations. Unplanned maintenance does," says Bhutiani. He believes that an on-condition maintenance program with no periodic shop visits produces some short-term benefits such as less work for shop crews and lower initial cost. But, these savings are eventually far-outweighed by the additional expense incurred in delays and cancellations, greater effort placed on line maintenance crews, and more expensive overhaul or repair once the unit comes off-wing. In addition, fleet operators often
must lease spare thrust reversers due to several units being unserviceable within a short period of time. While regular reverser inspections can help keep planes in the air, the inspections themselves use precious time — time out of service and time that a mechanic could doing something else. To avoid wasting time on unnecessary checks, ask your reverser OEM to provide a Work Scope Planning Guide (WSPG). These guides provide a comprehensive checklist for routine inspection and maintenance based on the needs of each fleet. "Every fleet flies different," says Timko. "Mechanics need to be aware of how reversers are being used if they want to inspect and maintain them efficiently."
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