Recently a member who flies in the vast MOA complex in Interior Alaska posed the question: “Would installing a transponder in my Super Cub make me more visible to military aircraft?” This prompted both some thought, and a few phone calls to colleagues. Like most things in aviation there are complexities and multiple situations to consider. Here is an attempt to break down the issue into several parts, specifically relative to the Interior Alaska section of the Joint Pacific Alaska Range Complex (JPARC). This contiguous set of MOAs and Restricted Areas starts near Fairbanks and extends east to just shy of the Canadian border, north to Fort Yukon and southward across the Alaska Range into the southcentral region, almost to Lake Louise.
Ground Based Radar: A transponder makes your aircraft more visible to ground based radars if you are in range and line of sight of the station. In addition to the FAA Air Traffic Control Radars at Murphy Dome (northwest of Fairbanks) and at Fort Yukon, the military has two radars— one just east of Eielson AFB, and the other on Donnelly Dome, south of Delta Junction. Military range and safety personnel monitor the radars which are compatible with our civilian transponders, while the Special Use Airspace is active. For the lower and mid-altitudes in which many GA aircraft operate, coverage should be good east and south of Fairbanks, around Delta Junction, on the north side of Isabel Pass and in the vicinity of Fort Yukon. As you fly farther east, in the vicinity of Tok, the Taylor Highway and upper Yukon Valley, you are probably not in ATC or military radar coverage. Also, if you operate south of the Alaska Range over the Denali and Richardson Highway areas, you will probably not be visible by either a military or civil ground based radar. Fortunately for us, that is not the only way military training aircraft may detect our presence.
TCAS Equipped Aircraft: A segment of the military fleet is equipped with a traffic collision avoidance system known as TCAS. Aircraft with this on-board system may detect an active transponder and be issued a warning if a potential collision threat exists. C-17’s and C-130’s are among the military aircraft that use this system. It works based on direct interaction between the two aircraft, without requiring ground based radar, or being in contact with a controller on the ground. It is important to note that the fighter aircraft typically involved in these training exercises don’t have TCAS.
Airborne Radar in Fighter: While not equipped with TCAS, many of the fighter aircraft do have other onboard radar systems to detect “threat” aircraft—and a transponder increases their ability to detect a civil aircraft.
Flying Surveillance Platforms: Another class of aircraft that sometimes operates in the airspace are the Airborne Warning and Control System aircraft, or AWACS. The original AWACS were Boeing 707s with what looked like a flying saucer mounted on their backs. Today additional models of aircraft are designed to provide airborne early warning and control. These are literally flying radar stations, with multiple means to track targets at considerable range. AWACS are routinely deployed during the major flying exercises, and are used during routine training in some sections of the JPARC. A transponder-equipped civil aircraft should be readily detected when AWACS are orbiting at altitude, and that information is passed on to other participating military aircraft if a safety issue arises.
Just as the weather can be benign, challenging or downright dangerous, the risk associated with Special Use Airspace also varies greatly. When planning to operate in the JPARC MOA complex, keep in mind the following categories and associated risk of encountering a military training aircraft.
Closed: About 100 days a year the ranges (both MOAs and Restricted Areas) are shut down. Typically, during weekends and holidays these airspaces are wide open to us.
Routine Training: Another ~240 days a year, the airspaces may be active, but at relative low levels of activity.
Major Flying Exercises: There are only about 40 days a year (could be up to 60 days max) when the major exercises like Red Flag and Northern Edge are conducted. These exercises routinely use AWACS, which are able to track transponder equipped aircraft within line of sight even at low altitude over the majority of the MOA complex. These exercises also represent the highest level of risk of encountering military aircraft operating in the ranges.
Don’t forget, whether you call them by phone before departure, or on the radio (125.3 MHz) after takeoff, the Special Use Airspace Information Service (SUAIS) operated by Eielson Range Control can tell you what level of activity to expect for the time and place you plan to fly.
Equipping with a Transponder: If you are not already transponder equipped, do careful research before investing. The mandate for equipping with ADS-B Out by 2020 is influencing transponder designs, as ADS-B communicates with the transponder. (At a future time we will explore the role ADS-B plays in the MOAs.)
While neither a transponder nor ADS-B Out will be required to fly in the JPARC, the transponder will certainly make you more visible to military aircraft in the MOAs. How much so depends on where, how high and when you fly!