Imagine being able to create an instrument approach while en-route, and then fly the approach down a minimum of 200 feet and 3/4sm. Not as crazy as it sounds. Here’s why:
IFR helicopters do this regularly, supporting the offshore petroleum industry in the Gulf of Mexico, flying as far as 200 miles offshore to land on ships, drill rigs, spars, and platforms. All in accordance with Advisory Circular 90-80B: Approval of Offshore Standard Approach Procedures (OSAP), Airborne Radar Approaches (ARA), and Helicopter En Route Descent Areas (HEDA). The title is certainly a mouthful, and the 58-page document can also be a little daunting. It helps to look at one in action, in this case the popular Copter Delta 30 OSAP, pronounced as “Oh-Sap.”
The Copter Delta 30 OSAP is one of five charted templates in AC90-80B that a pilot can adapt to almost any location offshore. It requires specific two pilot crew training, GPS, ground mapping capable radar, and radio/radar altimeter. It is a SIAP (special instrument approach procedure), and therefore also requires FAA authorization.
While en-route, destination weather is rechecked via radio or satellite phone. If the destination doesn’t have approved weather reporting, normally required under part 135, some operators have an FAA authorization to use remote reporting stations. Operations Specifications are regulatory and issued by the FAA, with some being more restrictive and some less restrictive than the associated FAR. Think of them as an extension of the FARs for specific operators. In this case the Op Spec is less restrictive, which is a good thing because although there are some AWOSs offshore, there never seem to be enough.
Wind condition at the destination is used to determine the approach course, which must be into the wind. A DWFAP (down wind final approach point) is typically created 7nm downwind from the destination, on the final approach course. The DWFAP can be created anywhere on the final approach course, as long as it is between 5 and 10nm from the destination. Depending on the en-route direction, a course reversal may be necessary in order to establish the helicopter inbound on course at the DWFAP. All this is planned and created while en-route, and then programmed into the Flight Management System or GPS. Radar in ground-mapping mode is used to determine there are no obstacles within .5nm of the final approach course. The final approach course can be adjusted for obstacles, just as long as it is within 10 degrees of the wind.
When 40nm or less from the destination, a cruise clearance is requested from ATC. This allows an immediate descent to MEA, an eventual descent to 900 MSL 20nm out, and a clearance to fly the approach and missed approach, if necessary.
Once established inbound at the DWFAP, at or below 70 knots (ground speed), a descent from 900MSL to 500MSL can be initiated.
If there are no obstacles within .5nm of course, and the radar and GPS are in agreement within .2nm for the destination target, a further descent from 500MSL to 200RA (radio altitude) can be made.
Radio altitude, from a radio or radar altimeter, is the actual height of the aircraft above the surface, in this case the ocean. The radio altimeter is used to determine the height, while the radar is used to identify obstructions. It’s a dynamic environment and just because an approach was clear of obstacles the day before doesn’t mean a drill ship wasn’t repositioned overnight.
At 1.1nm out, a right or left 30-degree turn is made to avoid overflying the destination, hence the name “Delta 30”. The heading change still has the aircraft converging with the destination, with the MAP (missed approach point) being .6nm away. At the MAP, one can proceed visually to land or go missed approach.
An OSAP is a great procedural tool for the trained two-pilot IFR crew in the offshore environment, providing precision approach-like minimums.
(These views and opinions are my own and do not necessarily reflect the views of Era.)