Increasing Use of GPS Technologies by Glider Pilots
GPS World has an article about the increasing use of GPS in aviation, especially with glider pilots. They talk about the use of a FLARM system which lets other pilots know of each others position through GPS. With about twenty mid-air collisions each year GPS is becoming an increasing asset in aviation.
The FLARM and other GPS systems use WAAS enabled GPS receivers to calculate present position and then predict location in a given amount of time based on velocity. Then other similarly equipped aircraft can receive positions of other aircraft as well as their projected flightpath.
“We selected the GPS receiver for different reasons besides size, power consumption, receiver sensitivity, price and availability,” stated Rothacher. “We were looking for a GPS with fast times-to-first-fix (TTFFs) from cold-start without any aiding (no almanac data, no ephemeredes data, no time, no rough location) to reduce the parts needed (battery, own real-time clock), with a PPS available and a GPS with Kalman filters that are suitable for our aviation movement models.
“Most inexpensive GPS are optimized for ground and vehicle applications, therefore vertical position, velocity, precision and stability are not adequately addressed. Even with the chipset we selected and in aviation dynamic modes, horizontal errors are reduced for the sake of vertical error.”
“To enhance the vertical data further, we built a second Kalman filter after the GPS’ own Kaman filter, where barometric and GPS-altitude data is dynamically corrected, partially based on VDOP and vertical accuracy estimates.
“It’s important that we have very little relative vertical error when two aircraft are close-by; absolute errors are not as important,” Rothacher added.
“Differential effects do not always help us because aircraft bank when flying a curve and this may produce different sky-views, so those two aircraft might base their GPS navigation solutions on non-identical sets of satellites, and the differential effect is lost.”
You can read the article here.