Sunday, December 1, 2013
The Rig Approach
Joint project involving Sikorsky and PHI ‘wrote the book’ with the S-92 automated rig approach for offshore operators.
|PHI-operated Sikorsky S-92 in the Gulf of Mexico.|
Having an instrument approach in the Gulf of Mexico is not news. That has been going on for more than 20 years using a system of navigation combining a Gulf of Mexico grid system, airborne radar, and more recently GPS, automatic dependent surveillance-broadcast (ADS-B) and of course radio contact that can be direct, altitude permitting, through company dispatchers and even satellite phone. The instrument approaches used by the operators have some things in common with land-based approaches used at most airports, but there are considerable differences as well.
The most glaring difference is that there is no runway in the middle of the Gulf. This means the approach must terminate in a block of “space.” There is limited en-route radar, no approach radar and no marker beacons. There are no lead in lights and no runway environment. There is always the possibility of movement on the water by boats within the approach area. When the helicopter breaks out, visual cues are restricted to seeing water, necessitating a lateral eye search for a destination platform.
FAA Advisory Circular, AC NO: 90-80B is the approving authority for three basic approach profiles; the Offshore Standard Approach Procedure (OSAP), Airborne Radar Approach (ARA) and Helicopter En route Descent Area (HEDA). Offshore operators are authorized to design the approaches they want to use, give it a name and then submit the write up to the FAA for approval. The approved approach will then be entered into that company’s Operations Manual.
|Treasure Swan TSRIG approach.|
Ron Doeppner, Sikorsky chief R&D test pilot, was designated as the lead for the project. The goal was to provide a coupled approach, using the OSAP type procedures that would bring the helicopter down to 200 feet above the water, with minimal or no control input by the pilot.
Analysis indicated that using the current system required as many as 17 separate decisions and actions, many taking place during the actual letdown. Seven take place after the IAF and three after the FAF. The other 10 can be done either before takeoff or prior to the IAF when properly planned.
Sikorsky went to work and provided the software and the hardware. The software was programmed into the S-92 Flight Control Computer (FCC) that will command the autopilot. The FCC does the math and the FMS gives the aircraft location and the destination. Platform final testing resulted in the 17 actions being reduced to seven. One of those is done prior to liftoff and the remaining six can be done during en-route flight.
The software has to know four things. 1) Where am I going? This means precise coordinates must be put into the Sikorsky FMS database using the center of the helideck as the target. This location is then given a waypoint designation. 2) Where is the wind? The destination rig or an AWOS station supplies that. 3) What will be the decision height (DH)? The pilot can program that. 4) Where will the offset to the platform be, left or right? Again, pilot programmed. These four parameters can be inputted any distance from the destination, however wind direction and speed should be done no more than 50 miles out to get good information. This means the pilot could now do a fully automated, hands-off approach including a MAP. He observes and monitors systems to ensure programmed performance. This is a big contribution to making an instrument approach safer.
|Sample of an OSAP approach.|
As mentioned earlier, the workload of the old OSAP requires many pilot inputs during the critical phases of the approach that can lead to distractions and it was felt that automating as many as possible would be a big safety advancement for offshore operations. Two OSAP approach plates show the differences in routes, check points, vertical and ground tracks and speeds. Onboard avionics consist of autopilot, FMS, FCC, ADS-B out, weather radar, radar altimeter, GPS and glass panel configurations such as RMI and other cue instrumentation.
In the approved Rig Approach, some of the depictions appear similar to the old OSAP and this is deliberate in that PHI requested that Sikorsky try to keep them close to the same to ease the approval process.
In a simplified explanation, the helicopter takes off from its shore base and proceeds to its GPS destination waypoint. As the pilot nears the waypoint, he presses an “Approach” button, the autopilot takes over and the helicopter begins a turn to the “turn point.” This FCC establishes this point based on wind direction previously entered by the pilot.
Think of it as an aligning point allowing the quickest transition from en route flight to the final approach fix. This is not a procedure turn, but rather a smooth turn for alignment. The helicopter continues at cruise speed and altitude until beginning a computed descent at 750 feet per minute timed to arrive at the turn point at 1,500 feet and 80 knots. Just before arriving at the IAF, it slows to 80 knots, stabilizes and levels off at 1,500 feet.
It then adjusts the ground speed to 80 knots as it proceeds to the IAF located two miles from the FAF, where it begins its final descent. The final approach course is off set to the left or right of the platform to present an obstacle free go around path. The two miles between the IAF and FAF gives the crew time to observe the approach area using the weather radar in ground mapping mode.
|Diagrams showing the Sikorsky and PHI-developed Rig Approach system.|
Sikorsky conducted the bulk of its certification flight testing in 2011 and followed that with a year of working with the FAA to provide a path for certification.
“Automated rig approach had never been done before so the FAA had no basis on which to compare it,” said Doeppner, Sikorsky’s project pilot. “We couldn’t go to the FAA regulators and say we’re certifying this according to existing data. We wrote the book on it, working with the operator (PHI) and the FAA.”
It is interesting that Sikorsky has put a new twist into helicopter use by designing an operational procedure that had been the bailiwick of the operators. I think that it was an inevitable direction to go in when you consider the sophistication of the computer systems that are being used in today’s larger and more expensive helicopters. The manufacturer will eventually produce a kit that can be retrofitted to the fleet, worldwide, and that will be an option on new purchases of S-92s. Plans are also in the works for equipping the S-76 fleet with the Rig Approach. The other OEMs will soon be developing their own versions of automated approaches for larger helicopters, it’s just a matter of time.
As Sikorsky says, this milestone culminates a five-year joint development effort between PHI and Sikorsky for Rig Approach. This new capability improves helicopter safety and operations for the offshore oil industry by reducing crew workload, increasing situational awareness and enhancing on-time performance,” said Carey Bond, President, Sikorsky Global Helicopters. “Safety is and always will be our priority. Innovations such as Rig Approach are invaluable, especially in the hostile weather environments where many of these rigs operate every day.”
Al Gonsoulin, CEO and Chairman of the Board of PHI states that: “We share an absolute commitment to continue to explore new technologies to enhance the safety of the men and women who work in the Gulf.”
Related: Offshore News