EV­ERY­THING EX­PLAINED

HERE’S WHAT ALL THOSE ACRONYMS RE­ALLY MEAN

Flying - - CONTENTS - By Richie Len­gel

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

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