First TCAS II-toting helo flying with Bristow

 - June 9, 2008, 6:47 AM

A Eurocopter AS 332 Super Puma, operated by Bristow in offshore oil transport in the North Sea, on April 9 became the first helicopter to be fitted with a second-generation Traffic Alert and Collision Avoidance System (TCAS II). The operator worked closely with equipment manufacturer Rockwell Collins to install the safety system aboard the 21-seat aircraft, with the assistance of Shell Aircraft. Bristow Eastern Hemisphere thus received the first EASA STC of TCAS II for rotary-wing aircraft.

According to Arnold Oldach, a Rockwell Collins marketing manager responsible for traffic and surveillance products, it was widely believed in the industry that helicopters were unsuitable applications for TCAS II: “These aircraft are slow; they do not have good climb rates; antennas would [suffer from rotor interference, presenting placement difficulties].”

Regardless of the perceived incompatibility of TCAS II and rotorcraft, Bristow began looking for solutions in 2004. “We realized there was no speed issue as TCAS II uses the time to closest point of approach to determine a threat. It does not use absolute speed. Additionally, there is a distance modulation mode that takes into account slow closure rates. TCAS II can detect one fixed-wing aircraft overtaking another one–thus proving it can be used at slow relative speeds,” Oldach said. Moreover, a climb rate of 1,500 fpm, like that achievable by Bristow’s helicopters, is consistent with TCAS II performance requirements.

The last obstacle was the location of the antenna installation. That was passed when engineers decided to use directional antennas on both the top and underside of the helicopters. Positioning the top antenna behind the main rotor was counter-intuitive. “We first looked at the engine cowlings, but they fold down to the side and so it would have been difficult to mount the upper aerial plinth in that location. We felt this could be a maintenance issue for the top antenna,” Oldach explained.

Another benefit of starting equipage with a big offshore operator is that it provides airline-like scrutiny of its operations, Oldach said. Bristow operates IFR helicopters in the offshore role, where 95 percent of the time they follow profiles similar to those of small IFR turboprop airliners. “There are 12 to 20 people aboard, they fly IFR at least one third of the time, often in IMC, they have scheduled flights and their typical cruise altitude is between 3,000 and 10,000 feet,” he pointed out.

Rockwell Collins believes rotorcraft TCAS II will save lives for a number of reasons. First, Bristow’s helicopters are intermixed with other rotorcraft and airplanes. There are 37,000 aircraft movements a year at Aberdeen Dyce airport in Scotland, the North Sea’s main platform for offshore transport. Helicopters use the same departure procedures and approach patterns as the other traffic. Oldach declined to provide a price for Rockwell Collins’s TCAS 4000, but he did maintain that TCAS II is affordable for virtually all operators. However, he conceded that it does not make sense for operators that fly VFR only. For those operations, TCAS I might provide sufficient situational awareness.

Rockwell Collins is now studying TCAS II installation on the Sikorsky S-92.