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Sunday, November 1, 2009

Flying the Sikorsky S-92A With the Rotor Ice Protection System

They Designed It, We Have It, Now What?

By Scot K. Penn, S-92 Supervisor, United Technologies Corp.

United Technologies Corp. routinely flies its RIPS-equipped S-92A aircraft in known icing conditions in the U.S.
CORPORATE/OPERATORS

For the past 36 months, I’ve had an exciting and challenging opportunity to fly the Sikorsky S-92A in the northeastern U.S. at the corporate flight department of United Technologies Corp. As one of the few pilots type rated in the S-92A who routinely flies the aircraft in known icing conditions in the U.S., I feel qualified to share some of the experiences that our flight department has observed.

My goal is not to teach how to operate the rotor ice protection system (RIPS), but to show how our Part 91 flight operation utilizes its capabilities. During the month of October 2008, I was called upon to help crew our S-92A on its flight to the National Business Aircraft Association (NBAA) display in Orlando, Fla. While showing the aircraft to a myriad of interested aviation professionals, the Rotor Ice Protection System (RIPS) was by far the most asked about system on the aircraft.

Following NBAA, I assisted the Sikorsky sales team and the Spectrum Health flight department from Grand Rapids, Mich., with the Air Medical Transport Conference (AMTC) S-76C++ static display in Minneapolis, Minn.

SIkorsky/UT Images
We also flew the S-92A to California in February 2009 for the Helicopter Association International (HAI) Heli-Expo conference. Making it through the Banning Pass at 10,000 feet in moderate ice was accomplished with ease. The controllers, and the fixed-wing aircraft flying in the area, were shocked that we were able to stay in the ice while the airplanes were vacating the altitude to escape the conditions. While showing the aircraft at the HAI conference, we were again bombarded with questions about RIPS.

This experience, coupled with the many questions about RIPS from the air medical community, as well as the attendees at the NBAA and HAI shows, compelled me to write this article. It is apparent that there have been many opinions and conclusions drawn concerning how and when RIPS can be utilized, or if it will be useful at all. I hope to shed some light on RIPS and its capabilities.

The flight operation at UTFlight routinely dispatches the S-92A into known icing conditions. There has been a steep learning curve associated with flying a helicopter in icing conditions, but RIPS has been a reliable system, and is very easy to use. In the automatic mode of operation, RIPS monitors the ice accretion rate from its two ice rate probes and cycles heat to the main and tail rotor blades. RIPS may also be selected to one of four “manual” modes of operation to immediately force the system to supply heat to the blades. The pilot monitors ice conditions on an ice rate meter located on the primary flight display (PFD) (see image on page 38).

Torque & Ice Rate Meter

Flight controls/hydraulic servos with ice accumulation..
According to the Sikorsky S-92A Rotorcraft Flight Manual (RFM), Volume One, the following limitations are associated with RIPS:

• Up to 10,000 feet pressure altitude.

• Flight into freezing drizzle/freezing rain/supercooled large drops (SLD) is prohibited.

• For flight into icing conditions, RIPS must be turned on.

Given these operational guidelines, I have piloted the S-92A in moderate and heavy icing on many occasions for time periods approaching 1.5 flight hours. Other pilots in the department have completed flights with longer duration in continuous ice conditions with only marginal increased power requirements being observed at any time.

The policy at UTFlight has alw     ays been to back up the helicopter flights during the winter months of operation with a fixed-wing aircraft, on the chance that the weather would prohibit the flight from being completed.

Since being placed into service July 2007, our S-92A has completed all of its assigned winter operation flights. In fact, we have actually seen an increase in number of flights dispatched because the S-92A now backs up our S-76C+ when icing could become a factor.

There are additional considerations that must be included in preflight planning. For example, is ground deicing available at both departure and arrival facilities? And, if shut down is necessary and subsequent deicing is needed, a tow bar may be required to move the aircraft.

RIPS can be manually cycled “on” while on the ground, providing the aircraft is running at 104–106 percent Nr .

Rotor engagement with ground ice accumulation could result in an ice shedding hazard.

Based upon available deicing options and length of time on the ground, a heated hangar could be an alternative.

Development of the S-92 RIPS began in 1997 and included three years of aircraft testing. That testing began with ice accretion trials at the Eglin Air Force Base McKinley Climatic Hangar in Florida and dry air tests of simulated ice on the tail surfaces in 2003. In 2004, Sikorsky conducted flight testing behind a CH-47D helicopter with special equipment that creates a cloud of ice in the air behind it. The tests ended with flights in natural icing conditions in 2004 and 2005 at sites from the northeastern U.S., through Canada to Alaska.
Flight under instrument conditions could be limiting, i.e., with the air traffic control system being saturated with aircraft, extended hold times can be expected on the ground and in the air.

Slick runways, taxiways, and helipads can be expected, and may not be cleared. Review winter landing and ground operations procedures.

ATC controllers have given unnecessary route and altitude changes for ice avoidance, but this has become less frequent as they have become more familiar with the capabilities of the S-92A equipped with RIPS.

In the end, most ground deice concerns can be avoided by continuing to run the aircraft and manually activating RIPS.

During conversations with various attendees at last year’s Air Medical Transport Conference, I was asked how many winter weather no-go flights I thought they could complete if they were in a RIPS-equipped aircraft. Earlier in my aviation career I was a pilot in southern Minnesota, flying helicopter emergency medical missions under single pilot instrument flight rules (SPIFR). I know the operational weather in the upper Midwest well. My answer to this hypothetical question is at least 75 percent of the flights could be completed, probably more. Having flown in the upper Midwest for approximately 12 years, I know that freezing drizzle, freezing rain and supercooled large drops are not a frequent problem within their area of operations. It is too cold!

RIPS is a safety tool that cannot have a price placed on it in any type of flight operation. The helicopter emergency medical service (HEMS) industry, in particular, has been overwhelmed with accidents and fatalities in recent months. Pilots need to be adequately trained and comfortable in the icing environment to safely conduct all weather missions.

Experience from the first two RIPS icing seasons have given Sikorsky the opportunity to Pareto (a model used to evaluate and improve) all RIPS components, enabling a strategic approach to system upgrades.

Main rotor blades have had heater mat improvements to the busbar/mat interface while a tail rotor blade sealant approach has improved the reliability of tail rotor ice shedding. The ice detection system (IDS) within RIPS has been improved from a health maintenance and diagnostic perspective, and all fielded S-92 aircraft were updated with this software in September 2008.

Horizontal stabilizer leading edge ice formation.
Sikorsky is proceeding with another round of system upgrades to further improve reliability of rotor blade harnesses and junction boxes while also working to further improve the RIPS health status page interface.

The Future

The Sikorsky S-76D is currently undergoing flight testing, and will be certificated with RIPS as an option when it is rolled out to the public. Configured for corporate, HEMS, or offshore operations, the Sikorsky S-76D helicopter equipped with RIPS will enhance safety and enable operators to complete missions in all-weather operations.

The RIPS installed on the S-76D model will be a mirror image of what we are using today on the S-92A, and will have the same capabilities of being dispatched into known icing conditions. When coupled with the new Pratt & Whitney Canada 210S engine with dual FADEC controls, state-of-the-art Thales cockpit, and onboard health and usage maintenance monitoring system (HUMMS), Sikorsky will have a capable “all-weather” S-76D model helicopter.

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