Late last month, the FAA published an Airworthiness Directive (2018-06-10) that requires a temporary revision to the HA-420 HondaJet's flight manual calling for pilot brake checks and replacing faulty brake valves upon condition. It was prompted “by reports of unannunciated asymmetric braking during ground operations and landing deceleration.”
On April 15 HondaJet N10XN, registered to GF Aviation, veered off the runway and into the grass while landing at Atlanta Peachtree DeKalb Airport (KPDK). Two days later, on April 17, HondaJet N166HJ, registered to KSI Business Aircraft, veered off the runway while landing at Iowa’s Harlan Municipal Airport (KHNR). The AD was published on March 29, before these incidents occurred, and became effective on April 13. According to Honda Aircraft, "The recent runway occurrences did not result in any injuries and the detailed investigation is still underway. We are dedicated to our mission to provide our customers with the utmost level of safety.”
In its AD, the FAA noted that a previous “investigation revealed that the power brake valve (PBV) housing design drawing dimension for a bore diameter, which serves as an O-ring gland outer diameter, is oversized from the Society of Automotive Engineers (SAE) specification guidelines for O-ring gland dimensions. The oversize bore allows back-up ring extrusion damage during normal operating hydraulic pressure in the valve, O-ring deformation/damage, and internal leakage of hydraulic pressure within the PBV from the master cylinder brake lines.
“The damage to the back-up ring and O-ring worsens during operation and causes the internal leakage rate of the PBV brake master cylinder lines to increase over time. This condition, if not addressed, could result in failure of the PBV, which could cause degraded braking performance and reduced directional control during ground operations and landing deceleration.”
In a statement provided to AIN, Honda Aircraft outlined steps that already have been taken. “We have initiated a service campaign to upgrade the supplier-provided power brake valve in all of our aircraft and are 63 percent through the process. The costs will be covered by Honda Aircraft and the supplier. Our goal is to minimize inconvenience to our customers and maintain our commitment to safety."
In February, Honda Aircraft revised its flight manual via Service Bulletin (SB-420-32-001) to include a new procedure for pilot checks of the brake system on the ground and before landing. It also contains instructions for corrective action in the event a leaking PBV is discovered. Honda Aircraft has fielded an improved-design PBV, and the AD requires replacement of the PBV with the new-design model if the installed PBV is found to be defective.
However, the FAA considers the AD to be an “interim action” and is considering mandating replacement of the existing PBV with the new design. It estimates the cost of replacing the PBV at $23,578. According to the AD, an estimated 72 HondaJets are on the FAA registry.