HERE’S WHAT ALL THOSE ACRONYMS REALLY MEAN
RNAV GPS approaches, Part 2
AIM 1-1-17 THROUGH 1-1-20, 1-2-1 THROUGH 1-2-3, 5-1-165-3-4, 5-4-5 THROUGH 5-4-7, P/C GLOSSARY, OPSPEC C052, FAA-H-8083-16, AC 20-138, AC 90-97, AC 90-100, AC 90-101, AC 90-105, AC 90-107, AC 90-108, TSO-C161, TSO-C162, TSO-C196, FAA ORDER 8260.19
1. GBAS (Ground Based Augmentation System), aka GLS (GBAS Landing System),
aka LAAS (Local Area Augmentation System). GBAS augments GPS and provides corrections to aircraft to improve GPS navigation for approaches. It is considered a
precision approach. LAAS is synonymous with GBAS. LAAS was the term initially used by the FAA, which has since migrated to the ICAO term GBAS. GLS is the FAA’s official term for a GBAS approach (e.g., GLS RWY 23).
GBAS and WAAS standards are different, so GBAS datalinks must be supported by compatible avionics in the aircraft. Pilots select a five-digit GBAS channel number within the FMS menu (or manually). Currently in use by several airlines at Newark, Houston and many other locations around the world.
2. Stand-alone GPS — Older nonprecision approach format. Example: GPS RWY 23
(very few are left). It is being replaced with a newer format prefaced by the acronym RNAV. Example: RNAV (GPS) RWY 23. 3. RNP, aka (RNAV) RNP, aka RNP AR — Required Navigation Performance with Authorization Required (AC 90-101). Special authorization from the FAA is required for these approaches, aka RNP SAAAR (Special Aircraft and Aircrew Authorization Required). 4. WAAS units are designed to evaluate the lowest minimums possible based on meeting required horizontal and vertical limits. The approach mode annunciator on the unit will notify you of which minimums you may use. Check for WAAS (D) notams. WAAS is required for LP, LPV, and LNAV/VNAV (without baro-VNAV) approaches.
5. Approved vertical guidance is available on LNAV/VNAV minimums, and existed before the WAAS system was certified. At that time, only aircraft equipped with a flight management system and certified baro-VNAV systems could use the LNAV/VNAV minimums. Today, LNAV/VNAV minimums may be flown using approved GPS WAAS receiver equipment.
6. Barometric aiding, aka baro-aiding, is an integrity augmentation that allows a GPS system to use a nonsatellite input source (e.g., pitot-static system) to provide vertical reference.
7. Barometric vertical navigation, aka baro-VNAV — Uses approach-certified barometric altitude info from the pitotstatic system and air data computer to compute vertical guidance (large aircraft). May be restricted by temperature.
8. RNAV approaches normally list several approach minimums to ensure as many aircraft as possible can fly the approach and provide operational flexibility if WAAS becomes unavailable. Aircraft with standard GPS receivers (or WAAS) can fly to the LNAV MDA. Aircraft with GPS and approach-certified Baro-VNAV can fly to LNAV/VNAV decision altitude (DA). WAAS-certified aircraft can fly to LP, LPV or LNAV/VNAV minimums. If for some reason WAAS becomes unavailable, all GPS or WAAS-equipped aircraft revert to the LNAV decision altitude.
9. Alternates — When using TSO-C129 and TSO-C196 (non-WAAS) GPS equipment at an alternate, authorized users may file based on a GPS-based IAP at
either the destination or the alternate airport, but not at both locations. When using TSO-C145 and TSO-C146 (WAAS) equipment at an alternate airport, planning must be based on flying the LNAV or circling minimum line, or GPS procedure, or conventional procedure with “or
GPS” in the title. Upon arrival at an alternate, LNAV/VNAV or LPV may be used to complete the approach. WAAS users with authorized baro-VNAV may plan for LNAV/VNAV DA, or RNP 0.3 DA at an alternate.
Types of RNAV (GPS) Integrity Limits: LNAV Larger than a localizer