Pression duct basse / haute / asymétrique (split) — lecture jauges L/R vs N1 et stages 5th/9th.Duct pressure low / high / split — L/R gauges vs N1 and 5th/9th stages.
ObjectifObjective
Interpréter la courbe duct vs %N1 et reconnaître un split anormal — sans confondre avec BLEED TRIP / PACK.Interpret the duct-vs-%N1 curve and recognize an abnormal split — without confusing BLEED TRIP / PACK.
DUCT PRESSURE NORMAL
Graphique CFM56-3B Sea Level : 5th stage PRSOV s’ouvre vers 50–60 % N1. 9th stage regulated ~32 ± 3 PSIG ; 5th ~42 ± 4 PSIG. Throttle retard : chute possible vers 22 PSIG avant réouverture high stage.CFM56-3B Sea Level chart: 5th stage PRSOV opens around 50–60% N1. 9th stage regulated ~32 ± 3 PSIG; 5th ~42 ± 4 PSIG.
On GND
Ground idle ~20 % N1 : duct 15–20 PSI pack ON. External ground air ≤ 50 PSI.
In FLT
Idle ~33 % N1 : duct 25–40 PSI.
DUCT PRESSURE ZERO
Bleed trip off sans voyant BLEED TRIP OFF rapporté — duct à zéro, OFV probablement full close. Avant descente rapide : essayer Trip Reset.Bleed trip off without a reported BLEED TRIP OFF light — duct at zero, OFV probably full close. Before a rapid descent: expect cabin rate changes.
DUCT PRESSURE SPLIT
~10 PSI : possible ACM — confirmer si split disparaît (300-500 mix full hot / 400 Trim Air OFF + temp full hot = bypass ACM).~10 PSI: possible ACM — confirm if the split disappears (300-500 mix full hot / 400 Trim Air OFF + temp full hot = bypass path).
Causes : Bleed Switch OFF ; High Stage failed / dispatched CLOSED ; fuite WING-BODY non détectée.Causes: Bleed Switch OFF; High Stage failed / dispatched CLOSED; undetected WING-BODY leak.
Affecte : pressu (min 18 PSI climb/cruise ; ≥ 10 PSI idle descent) ; engine/wing AI (High Stage suspect → ≥ 60 % N1 en icing) ; hyd pump ; NGS ; water lav/galley.
DUCT PRESSURE HIGH
Ne pas dépasser 50 PSI. 60–80 PSI à haut N1 → PRSOV malfunction.Do not exceed 50 PSI. 60–80 PSI at high N1 → PRSOV malfunction.
On GND : MEL 36-05 (Bleed INOP) ou 36-09 (9th Stage CLOSED).
In FLT : fermer Bleed en climb pour < 50 PSI ; cruise ON (40–50) ; envisager fermer en approche (go-around).In FLT: close Bleed in climb for < 50 PSI; cruise ON (40–50); consider closing on approach (go-around).
High Stage INOP : 60 % N1 seulement en icing. Idle sans icing : jusqu’à 55 % N1 pour pressu. Fuel MEL 36-09 : +2 % courts / +1 % longs ; MEL 30-03 EAI OPEN +1.3 %. TOD ≈ 4 × (Alt÷1000) à 60 % N1 (~1 500 fpm).High Stage INOP: 60% N1 only in icing. Idle without icing: up to 55% N1 for pressurization. Fuel MEL 36-09: +2% short sectors as applicable.