LNAV / VNAV • Automatic Flight

AFDS

ConditionCondition

Modes LNAV / VNAV — latéral et vertical FMC via AFDS ; interaction MCP, FMA et A/T.LNAV / VNAV modes — FMC lateral and vertical via AFDS; MCP, FMA and A/T interaction.

ObjectifObjective

Distinguer LNAV vs HDG SEL vs VOR LOC, VNAV PTH/SPD vs LVL CHG/V/S, et le plafond ALT MCP.Distinguish LNAV vs HDG SEL vs VOR LOC, VNAV PTH/SPD vs LVL CHG/V/S, and the MCP ALT ceiling.

LIVE Push LNAV / VNAV · lire FMAPush LNAV / VNAV · read FMA

Schéma modes FMC ↔ AFDSFMC ↔ AFDS mode schematic

FMC fournit la trajectoire ; MCP arme ; FCC vole ; FMA confirme.FMC supplies path; MCP arms; FCC flies; FMA confirms.

LNAV

Suit la route active FMC (legs) — pas le heading bug.Tracks the active FMC route (legs) — not the heading bug.
Armable au sol ; capture en vol selon écart / logique d’armement.Armable on ground; captures in flight per deviation / arming logic.
FMA colonne latérale : LNAV actif (vert) quand capturé.FMA lateral column: LNAV active (green) when captured.
Perte LNAV → HDG SEL ou VOR LOC selon besoin ; reconstruire route CDU.LNAV loss → HDG SEL or VOR LOC as needed; rebuild CDU route.
Approche LNAV : utile si course selector / VOR-ILS OOS (workaround MEL 34-17) — dest / alt / enroute alt doivent offrir LNAV.LNAV approach: useful if course selector / VOR-ILS OOS (MEL 34-17 workaround) — dest / alt / enroute alt must offer LNAV.
P-RNAV : un A/P (FCC) suffit (SOP) — dual toujours pour Autoland ILS.P-RNAV: one A/P (FCC) enough (SOP) — dual still for ILS Autoland.

VNAV

VNAV PTH

Suit le path vertical FMC (contraintes, idle path, etc.).Follows FMC vertical path (constraints, idle path, etc.).
Altitude MCP reste le plafond / contrainte sélectionnée équipage.MCP altitude remains the crew-selected ceiling / constraint.

VNAV SPD

Priorise la vitesse (souvent montée) plutôt que le path exact.Prioritizes speed (often climb) over exact path.
Lire la colonne pitch — ne pas assumer PTH.Read the pitch column — do not assume PTH.

SPD INTV / ALT INTV (as installed) : intervention temporaire sans quitter VNAV.SPD INTV / ALT INTV (as installed): temporary intervention without leaving VNAV.
Si VNAV refuse : perf/init, contraintes, ALT MCP trop bas/haut, discontinuities.If VNAV refuses: perf/init, constraints, MCP ALT too low/high, discontinuities.
Transition vers LVL CHG / V/S / ALT HOLD si intervention MCP manuelle requise.Transition to LVL CHG / V/S / ALT HOLD if manual MCP intervention required.

Interactions A/TA/T interactions

Mode	A/T typique	NoteNote
VNAV climb	N1	Limite N1 FMC (sauf A/T LIM)FMC N1 limit (unless A/T LIM)
VNAV cruise	N1 / SPEED	Selon thrust mode / economyPer thrust mode / economy
VNAV descent	ARM / SPEED	Souvent idle path + speed windowOften idle path + speed window
LVL CHG climb	N1	Vers ALT MCPToward MCP ALT
LVL CHG desc	SPEED / idle	Surveille underspeedWatch underspeed

Checks équipageCrew checks

CDU : RTE active, pas de discontinuity non voulue, perf OK.CDU: active RTE, no unwanted discontinuity, perf OK.
MCP : ALT correct (contrainte / clearance) ; IAS cohérent.MCP: correct ALT (constraint / clearance); coherent IAS.
Push LNAV / VNAV → FMA armé puis capturé.Push LNAV / VNAV → FMA armed then captured.
Si A/T LIM + symptômes TAT → croiser sonde température.If A/T LIM + TAT symptoms → cross-check temp probe.

LNAV vs HDG SEL vs VOR LOCLNAV vs HDG SEL vs VOR LOC

Mode	SourceSource	Quand l’utiliserWhen to use
LNAV	FMC legs	SID/STAR/RTE, approche LNAV, RNAVSID/STAR/RTE, LNAV approach, RNAV
HDG SEL	MCP heading	Vecteurs ATC, recovery perte LNAVATC vectors, LNAV-loss recovery
VOR/LOC	Nav radio	VOR track / LOC avant APP completVOR track / LOC before full APP
LOC	ILS	Après APP — capture localizerAfter APP — localizer capture

VNAV vs LVL CHG vs V/SVNAV vs LVL CHG vs V/S

Mode	PilotageGuidance	PlafondCeiling
VNAV PTH/SPD	FMC	MCP ALT + contraintes
LVL CHG	Thrust/speed vers ALTThrust/speed toward ALT	MCP ALT
V/S	Thumbwheel	MCP ALT (capture)
ALT HOLD	MaintienHold	Altitude actuelle

Scénarios teachingTeaching scenarios

Climb clearance : ALT MCP → VNAV ou LVL CHG → FMA VNAV SPD/PTH ou LVL CHG + A/T N1.Climb clearance: MCP ALT → VNAV or LVL CHG → FMA VNAV SPD/PTH or LVL CHG + A/T N1.
Level-off hand-fly : garder A/T — SPD ou ARM (N1) — pas Alpha Floor.Hand-fly level-off: keep A/T — SPD or ARM (N1) — not Alpha Floor.
Descend via : VNAV PTH ; si path invalide → LVL CHG / V/S + surveillance vitesse.Descend via: VNAV PTH; if path invalid → LVL CHG / V/S + speed watch.
Intercept LOC : LNAV ou HDG → APP → FMA LOC armé → capture ; COURSE = QFU.LOC intercept: LNAV or HDG → APP → FMA LOC armed → capture; COURSE = QFU.

Fenêtre altitude MCP = plafond — toujours avant le mode vertical.MCP altitude window = ceiling — always before vertical mode.

LNAV/VNAV = teaching AFDS. Pour switches LIVE → simulateur MCP. FMC détail → chapitre FMC/CDU.LNAV/VNAV = AFDS teaching. For LIVE switches → MCP simulator. FMC detail → FMC/CDU chapter.

FMA · MCP · Système · Course / MEL 34-17FMA · MCP · System · Course / MEL 34-17