During a technical briefing held yesterday at Heli-Expo, Eurocopter encouraged EC 135 operators to keep a close eye on their helicopters’ main transmission gearbox. The European helicopter manufacturer, along with transmission supplier ZF Luftfahrttechnik of Flugplatzstrasse, Germany (Booth No. 4349), is taking a proactive approach to prevent spalling or tooth breakage of the input drive gears.
While Eurocopter technical representative Mike Morters said that since 2004 only five of the more than 600 in-service EC 135s have experienced gearbox tooth breakage, all of which led to chip light warnings, the company is concerned about the situation and is watching the fleet for evidence of any further problems. “Our priority is to keep the fleet flying without compromising flight safety,” he told operators.
Morters explained the four stages of input drive gear deterioration, with Stage 4 being the most serious. Stage 1 involves “grey staining” of the gear teeth–micropitting that lessens the smoothness of the teeth and increases friction. The second stage can be identified by gray staining combined with pitting. According to Morters, gray staining and pitting are not “rejection criteria,” though he noted that more severe pitting could be.
Once the deterioration progresses to the Stage 3 (gray staining combined with spalling), things started getting more expensive since spalling is cause for part replacement. Stage 4 is a further deterioration of severe pitting or spalling that leads to tooth breakage and results in metal chips in the transmission fluid.
To combat wear of the main transmission gearing, Eurocopter recommends that all EC 135 operators switch to Castrol Transmax high-performance transmission oil per SB EC135-63-011; maintain the proper oil transmission level (ASB 63A-010 increased the transmission oil quantity by two liters); and regularly have transmission oil samples analyzed by Jet-Care International (Booth No. 2737). Representatives of Eurocopter, ZF Luftfahrttechnik and Jet-Care are available on the show floor to field any questions EC 135 operators have about the transmission wear seen in the helicopter model.