Almost all high-altitude flights are made using mountain lee waves. As covered in Chapter 9, Soaring Weather, lee wave systems can contain tremendous turbulence in the rotor, while the wave flow itself is usually unbelievably smooth. In more recent years, the use of lee waves for cross-country soaring has led to flights exceeding 1,500 miles, with average speeds of over 100 mph. [Figure 10-31]
The amount of preflight preparation depends on the height potential of the wave itself. Assume that the pilot is planning a flight above 18,000 feet MSL during the winter. (Pilots planning wave flights to much lower altitudes can reduce the list of preparation items accordingly.)
At all times during flights above 14,000 feet MSL, and for flights of more than 30 minutes above 12,500 feet MSL up to and including 14,000 feet MSL, 14 CFR states that required crewmembers must use supplemental oxygen. Pilots must be aware of their own physiology; however, it may be wise to use oxygen at altitudes well below 14,000 feet MSL. In addition, pilots should recognize signs of hypoxia.
When flying at higher altitudes, the inside of the glider can get cold. The portions of your body exposed to the sun through the canopy might feel comfortable but your feet will probably feel the temperature drop and could get cold. It is important to prepare for this and pack thermal underwear, wear warm socks and shoes and have gloves easily accessible during the flight.
Within the continental United States, Class A airspace lies between 18,000 and 60,000 feet MSL (flight level (FL) 180 to FL 600). Generally, flights in Class A airspace must be conducted under instrument flight rules (IFR). However, several clubs and glider operations have established so-called wave windows. These are special areas, arranged in agreement with air traffic control (ATC), in which gliders are allowed to operate above 18,000 feet MSL under visual flight rules (VFR) operations. Wave windows have very specific boundaries. Thus, to maintain this privilege, it is imperative to stay within the designated window. On any given day, the wave window may be opened to a specific altitude during times specified by ATC. Each wave window has its own set of procedures agreed upon with ATC. All glider pilots should become familiar with the procedures and required radio frequencies.
True airspeed (TAS) becomes a consideration at higher altitudes. To avoid the possibility of flutter, some gliders require a reduced indicated never-exceed speed (VNE) as a function of altitude. For instance, the Pilot’s Operating Handbok (POH) for one common two-seat glider, list a VNE at sea level of 135 knots. However, at 19,000 feet MSL, it is only 109 knots. Study the glider’s POH carefully for any limitations on indicated airspeeds.
There is always the possibility of not contacting the wave. Sink on the downside of a lee wave can be high—2,000 fpm or more. In addition, missing the wave often means a trip back through the turbulent rotor. The workload and stress level in either case can be high. To reduce the workload, it is a good idea to have minimum return altitudes from several locations calculated ahead of time. In addition, plan for some worse case scenarios. For instance, consider what off-field landing options are available if the planned minimum return altitude proves inadequate.
A normal preflight of the glider should be performed. In addition, check the lubricant that has been used on control fittings. Some lubricants can become very stiff when cold. Also, check for water from melting snow or a recent rain in the spoilers or dive brakes. Freezing water in the spoilers or drive brakes at altitude can make them difficult to open. Checking the spoilers or dive brakes occasionally during a high climb helps avoid this problem. A freshly charged battery is recommended, since cold temperatures can reduce battery effectiveness.
Check the radio and accessory equipment, such as a microphone in the oxygen mask even if it is not generally used. As mentioned, the oxygen system is vital. Other specific items to check depend on the system being used.
A briefing with the tow pilot is even more important before a wave tow. Routes, minimum altitudes, rotor avoidance (if possible), anticipated tow altitude, and eventualities should be discussed on the ground prior to flight.
After all preparations are complete, it is time to get in the glider. Some pilots may be using a parachute for the first time on wave flights, so become familiar with its proper fitting and use. The parachute fits on top of clothing that is much bulkier than for normal soaring, so the cockpit can suddenly seem quite cramped. It takes several minutes to get settled and organized. Make sure radio and oxygen are easily accessible. If possible, the oxygen mask should be in place, since the climb in the wave can be very rapid. At the very least, the mask should be set up so that it is ready for use in a few seconds. All other gear (mittens, microphone, maps, barograph, etc.) should be securely stowed in anticipation of the rotor. Check for full, free rudder movement since footwear is probably larger than normal. In addition, given the bulky cold-weather clothing, check to make sure the canopy clearance is adequate. The pilot’s head can break a canopy in rotor turbulence, so seat and shoulder belts should be tightly secured. This may be difficult to achieve with the extra clothing and accessories, but take the time to ensure everything is secure. There will not be time to attend to such matters once the rotor is encountered.