J  Pilot/Controller Glossary Pilot/Controller Glossary  8/15/19 1/30/20  JAMMING- Denotes emissions that do not mimic  Global Navigation Satellite System (GNSS) signals  (e.g., GPS and WAAS), but rather interfere with the  civil receiver's ability to acquire and track GNSS  signals. Jamming can result in denial of GNSS  navigation, positioning, timing and aircraft depen- dent functions.  JET BLAST- The rapid air movement produced by  exhaust from jet engines.  JET ROUTE- A route designed to serve aircraft  operations from 18,000 feet MSL up to and including  flight level 450. The routes are referred to as “J”  routes with numbering to identify the designated  route; e.g., J105.  JET STREAM- A migrating stream of high-speed  winds present at high altitudes.  JETTISONING OF EXTERNAL STORES- Air- borne release of external stores; e.g., tiptanks, ordnance.  JUMP ZONE- The airspace directly associated with  a Drop Zone. Vertical and horizontal limits may be  locally defined.  JOINT USE RESTRICTED AREA- (See RESTRICTED AREA.) (See FUEL DUMPING.) (Refer to 14 CFR Part 91.) (See Class A AIRSPACE.)  (Refer to 14 CFR Part 71.)  PCG J-1 