NTSB Factual Report

On November 19, 2015, about 1150 Pacific standard time, an air ambulance Airbus EC-135P2+ helicopter, ingested foreign object debris (FOD) into the Fenestron during an approach to the Victor Valley College Regional Public Safety Training Center in Apple Valley, California. The commercial pilot and four passengers were not injured, and the helicopter sustained substantial damage. The helicopter was registered to and operated by Reach Air Medical Services LLC, Santa Rosa, California, under the provisions of 14 Code of Federal Regulations Part 135 as a day, visual flight rules passenger flight. Visual meteorological conditions prevailed and a company visual flight rules flight plan was filed. The flight originated from the Victor Valley College Regional Public Safety Training Center in Apple Valley, California.

Note: Various photos and diagrams of the Airbus EC-135 Fenestron, including labeling of the various parts, is located in the public docket of this accident under the Airbus EC-135 Fenestron Hub Fairing Report.

According to the pilot, the helicopter was being utilized for training with firefighting personnel to simulate patient loading and unloading. The training consisted of multiple takeoffs and landings from the training center landing site. He reported that during the third landing, between two to three feet above ground level, he felt the helicopter "shutter unexpectedly." The pilot immediately landed and shut down the helicopter without further incident.

A postflight inspection revealed that a towel had been ingested into the Fenestron. The pilot reported that the towel migrated from an unsecured storage container near the landing site. The helicopter sustained substantial damage to the Fenestron tail rotor blades, the Fenestron housing body, the tail boom, and the tail rotor drive shaft flex couplings. During the course of the investigation, it was discovered that when the towel was ingested, the Fenestron hub fairing detached from the hub body and it was ingested by the Fenestron tail rotor blades.

The director of maintenance (DOM) for the operator reported that the tail rotor gearbox was shipped to the manufacturer for an inspection. Additionally, the DOM reported that all of the main rotor blades, "received a small amount of FOD damage at middle cord line near the tips" and that the "damage was the result of FOD from the Fenestron [hub fairing ingestion] after the towel was ingested."

The pilot reported there were no preimpact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation.

WRECKAGE AND IMPACT INFORMATION

Photos supplied by the operator showed pieces of the towel attached to various stators in the Fenestron housing body. Large gouges in the Fenestron housing body were present, consistent with impact from FOD. Small gouges were also present on the various Fenestron tail rotor blades, consistent with impact from FOD. The Fenestron hub fairing was not attached in the photos. A photo of the Fenestron hub fairing displayed it in numerous pieces, consistent with being destroyed by the impact of the Fenestron tail rotor blades.

ADDITIONAL INFORMATION

Safety Recommendation NORW-2007-073

In 2007, the Accident Investigation Board Norway (AIBN) along with the European Aviation Safety Agency (EASA) filed a formal safety recommendation to Eurocopter (Airbus) regarding the design of the Fenestron hub fairing. This safety recommendation was based on an Airbus EC-135 accident (2007/35) that occurred in Liagardene, Norway in 2006, which sustained similar damage due to similar accident sequence events. This safety recommendation from the AIBN states in part;

The accident has revealed that the hub cover of the Fenestron on EC-135 can loosen when the rotor tips are bent out. A loosened cover will be sucked through the Fenestron and cause extensive damage. AIBN recommends that Eurocopter consider whether the fixing mechanism between the cover and hub could be changed to prevent loosening.

The response from EASA states in part;

EASA agrees with this recommendation. Eurocopter Deutschland (ECD) has launched a technical review of possible design improvements to the Fenestron hub cap installation; this might lead to a future design change if deemed suitable. However, no unsafe design features have been identified so far. In-flight loss (as well as all other three events reported to ECD) was accompanied by contact of the Fenestron/tail boom with obstacles.

This safety recommendation was closed out with no further action. After multiple requests, the manufacturer did not respond to inquiries from the National Transportation Safety Board investigator-in-charge concerning what actions have been taken regarding the inadequate design of the Fenestron hub fairing attachment.

Airbus EC-135 Fenestron Hub Fairing Information

The Fenestron hub fairing is attached to the hub body with six attachment hardware assemblies. These hardware assemblies are inserted inside of a lip in the hub body, which covers the entire hub body. Once the hardware assemblies are inserted inside of the lip in the hub body, the screws are then tightened by a mechanic. A bore is located at the center of the fairing to aid with detachment, and is sealed with a plastic plug.

Various photos, diagrams, and historical Airbus Fenestron FOD ingestion accident/incident information is located in the public docket of this accident under the Airbus EC-135 Fenestron Hub Fairing Report.

NTSB Probable Cause

The ingestion of a towel from an unsecured storage container at the landing site into the helicopter's fenestron during the landing.