Eurocopter EC130 N155GC accident near Peach Springs, Arizona

Probable cause

A loss of tail rotor effectiveness, the pilot’s subsequent loss of helicopter control, and collision with terrain during an approach to land in gusting, tailwind conditions in an area of potential downdrafts and turbulence.

NTSB analysis

The pilot of the helicopter was conducting his third air tour flight of the day, transporting six passengers to the operator's plateau landing site, known as Quartermaster, on the south bank of the Colorado River within the Grand Canyon. He was appropriately rated for this flight and was experienced executing approaches and landings at Quartermaster. Following an uneventful flight to the area, the pilot began a descent and approach from across the river to a ravine on the west side of the landing site. The accident helicopter was the ninth of ten helicopters scheduled to land at the site that afternoon, and because all of the pads on the east side of the site were occupied, the pilot initiated a descending left turn toward a landing pad located on the west side of the site, aligning the helicopter on an east-northeasterly heading. Photographs of the landing site windsock near the time of the accident indicated winds at magnitudes of 15 kts or greater from the north-northwest, resulting in tailwind conditions during approaches to the west pads. A pilot on the ground at the landing site reported that the accident helicopter began to decelerate as it approached the landing pads and entered a nose-up attitude, then turned left toward the landing pads, transitioned through several pitch oscillations, and drifted aft. The left turn continued through 720° of rotation before the helicopter descended into a canyon just west of the landing pads and impacted terrain. Photos indicated that the helicopter’s final impact in the canyon was immediately followed by a postcrash fire. Postaccident examination of the helicopter and engine revealed no evidence of mechanical anomalies that would have precluded normal operation.

Two pilots who landed just before the accident conducted their approaches in a similar direction as the accident pilot and both later reported that they encountered adverse wind. The pilot who landed just before the accident reported that he encountered wind conditions that necessitated full right pedal and nearly resulted in a loss of yaw control. The accident helicopter’s flight characteristics at the time of the accident would have included slowing airspeed, a high power setting, and a relative wind position that were all conducive to a loss of tail rotor effectiveness (LTE), thus it is likely that the loss of control was the direct result of LTE.

The landing site was located on a plateau and provided limited approach options due to its local topography. At the time of the accident, potential demarcation lines (boundaries of updrafts and downdrafts) would have been on the pinnacles of ridges located along the approach to the Quartermaster west pads. Figure 8 shows a conceptual illustration of potential demarcation lines and wind directions based on the terrain and wind environment present around the accident site at the accident time, and suggests areas where downdrafts, updrafts and turbulence could have impacted the accident flight’s approach to the landing site.

Figure 8. Conceptual display of demarcation lines at accident site

The proximity of other pilots and passengers who witnessed the accident resulted in an immediate response to aid the occupants of the helicopter; however, the remote location of the accident site and communication difficulties between on-scene and outside resources made rescue coordination challenging and victim transport by helicopter to the hospital did not begin until about 6 hours after the accident. Although all seven occupants survived the impact, they all sustained significant burn injuries, and three of the occupants were likely unable to egress the helicopter. The most significant factor affecting occupant survival was the immediate postcrash fire. The accident helicopter was not equipped, nor was it required to be equipped, with a crash-resistant fuel system. Due to a lack of data regarding the crash dynamics and impact forces, the effectiveness of such a system, if installed, in delaying the onset of a postcrash fire could not be determined.

The only source of local wind information at Quartermaster at the time of the accident was a windsock, which can only display wind speeds up to 15 kts. Further, windsocks cannot indicate the presence of downdrafts, turbulence, or any other local environmental conditions that may affect flight safety, particularly when landing in a confined area.

The operator provided its pilots with a morning weather briefing on the day of the accident, which advised of gusty wind conditions in the area of the accident site forecast to increase throughout the afternoon. Weather advisories issued after the morning weather briefing, several hours before the accident, indicated a cold front proceeding through the area of the accident site with associated wind gusts and turbulence. This information was likely not captured by the operator and distributed to its pilots even though some of the forecasts included wind conditions above the maximum wind outlined in the company's general operations manual (GOM). Because there was no additional wind information at the landing site beyond the windsock, it could not be determined the actual wind conditions at the landing site at the time of the accident; however, pilots who landed before the accident pilot estimated the wind to be 15 to 20 knots, which is below that specified in the GOM. Although the morning briefing was not intended to be the pilots' sole source of weather information, it was likely the primary weather information the accident pilot received before the accident, as he had recently flown to Quartermaster and is not likely to have rechecked the weather.

Text from the NTSB. Open the NTSB docket for WPR18MA087 for the full record.