Friday, July 1, 2005
Military Spin: Help With Brownouts, Part 2
This time we'll talk less tech and more technique to get into the dusty zone when you don't have the equipment discussed in my last article ("Help With Brownouts," March 2005, page 42). The following approach parameters approximate Black Hawk performance and must be tailored to conditions and your aircraft weight and disk loading.
The factors that most effectively counteract dust clouds are wind, approach angle and speed. There is a certain wind velocity that allows touchdowns with the dust behind the cockpit. It roughly corresponds to translational lift airspeed. Approach speed should be planned to include the prevailing wind. Subtract a portion of the wind from your planned indicated airspeed. If translational lift speed is 18 kt. and winds are 8 kt., shoot the approach at 10 kt. or more ground speed just prior to touchdown to stay ahead of the cloud.
The elevation and temperature prompts will cue you for a go-around power assessment. You must have go-around power! It's then critical to evaluate or assess the soil composition as part of your area recon. A good question to ask is: Is this a dry river or lake bed that might produce fine dust? Crews also should seriously consider the landing zone size to afford run-on and go-around maneuvering room.
Planning the go-around should include the clearest escape route prior to committing to the approach. This heading should be verbalized in the event that an instrument takeoff is required due to lost visual references in the dust cloud. The area assessment should include at least one prominent visual reference. A useful nighttime tool for this is a cluster of chemical light sticks tied to a heavy weight tossed into the zone during a low recon. A useful commercial product for unaided and night-vision goggle-compatible LZ marking options is the Powerflare (www.powerflare.com). After the recon is finished and references are established, determine the approach angle technique you plan to employ. Depending on terrain and landing gear tolerances, you may choose a steep and slower approach (Fig. 1) or a normal to shallow angle and fast approach (Fig. 2) with a planned run-on at translational lift. For the steep approach, fly the angle to keep the reference at an apparent 45 deg. angle flying the "trans lift burble" all the way down. Crew calls from the cabin can provide advance warning on the cloud propagation before it engulfs the cabin. Calls like "Cloud starting to form," "Cloud at the tail," "Cloud at the cabin," alert the pilot that he's about to lose references. Depending on speed and touchdown spot location, he may elect to go around and try differing approach angle and speed combinations to minimize the cloud's effects. Landing speed should be just fast enough to minimize the cloud's effects, but the cloud may engulf the aircraft just as the gear touches the ground. A prominent visual reference is critical for this approach style.
Like most helicopter operations, the combination of ground speed and approach angle varies. It can be very disorienting to accept the cloud and maintain a drift-free approach through the cloud to the ground, but it's feasible with appropriate visual cueing systems or a prominent ground reference and a go-around plan. Successful completion of the steep approach is done with a continuous collective reduction during the ground effect cushion to prevent a disorienting hover in the "goo."
Searchlights employed at night can exacerbate the "inside-a-ping-pong-ball" effect and should only be used when absolutely necessary. If lighting must be used, aim it where it won't reflect directly back into the pilot's eyes. "Pixie dust" is a strange phenomenon often encountered during night brownout landings. Small particles striking the leading edge of the blades create millions of sparks that produce an eerie, disk-shaped sparkling glow around the rotor. The effect is visible to the NVG-aided and unaided eye, can produce spatial disorientation, and must be anticipated.
If unable to execute a safe brownout landing, start the go-around with alignment on the pre-briefed heading while minimizing side drift. Climb immediately with three positive and verbalized climb indications i.e. vertical velocity, altimeter and radar altimeter until you've exited the cloud.
I hope this has given you some tools for your flying toolbag. Crews should practice these techniques for proficiency in conditions without brownout so they'll be ready when needed.
My thanks to the folks at Marine Aviation Weapons and Tactics Sqdn. 1 at MCAS Yuma, Ariz. and at the Navy's Weapons and Tactics Instructor course at NAS Fallon, Nev. for their inputs.