Battery-Only Flight and the Degradation Picture

The last rung of the degradation ladder: the EMER GEN is also unavailable, and the whole aircraft runs on two 40 Ah batteries. This article does two things — it works through the FCOM "batteries only" segments (flight and ground), and, as the close of the failure chapter, it redraws the degradation ladder set out in the overview with the detail of the fault articles 21–29: a complete recap of the chapter's failure face.

By the end you should be able to answer five questions: (1) on batteries only, which buses still have power, and why is the SHED family entirely gone? (2) what differs on either side of the ground 50 kt split? (3) what are the three conditions for the discharge horn? (4) what is the complete ladder from normal to batteries-only (the warning name / remaining / article for each rung)? (5) what instruments are you left with in this configuration?

1. Flight with batteries only

"When emergency generator is not available, the batteries supply: the DC ESS BUS, the DC LAND RECOVERY (whatever the LAND RECOVERY pushbutton position is), and through the STAT INV: the AC ESS BUS, the AC LAND RECOVERY (whatever the LAND RECOVERY pushbutton position is). The AC ESS SHED, the DC ESS SHED and the SHED LAND RECOVERY are not supplied. The AC ESS GND is lost."

Per FCOM DSC-24-10-30-30. Three reading points:

1. The LAND RECOVERY buses are supplied on batteries only, whatever the pushbutton position (407PP permanently supplied) — the FCOM states only this fact (the "landing kit does not wait for a pushbutton" causal framing is a teaching reading, not FCOM text). The FCOM also notes the ground batteries-only ELEC AC ECAM page is identical to the flight one.
2. The SHED segments are all gone — the 2.5 kVA budget only covers the ESS core. The static inverter, "soldiering on" on its five protections, is the entire AC source (see Static Inverter).
3. The DC BAT BUS is lost after 7 s in this configuration (the distribution-table footnote — the end of the battery bridge, see Batteries and the BCL).

Remaining instruments (an integrative read of Static Inverter, Monitoring and Indication and EMER CONFIG): PFD 1 (the core), ISIS, VHF 1, and the battery voltmeter — the "all-black master instrument" of the monitoring article, now centre-stage: select 1/2 in turn and watch for > 25 V. The FCTM's RAT-scenario cautions all apply, and more strictly: out of roll trim / manual trim / no anti-skid — one notch tighter than the RAT column of the EMER CONFIG two-state table.

2. On the ground, batteries only, and the 50 kt split

"Provided they are both selected AUTO, batteries supply the: DC ESS BUS, DC BAT BUS, DC LAND RECOVERY … And, through the static inverter, the: AC ESS BUS, and AC ESS GND, AC LAND RECOVERY …"

Per FCOM DSC-24-10-30-30. Two differences from the flight version: it gains DC BAT BUS (at low ground speed the battery feeds 3PP directly — the V ≤ 50 kt row of the distribution table) and AC ESS GND (905XPB, supplied only on the ground — see AC Distribution).

The 50 kt split has been built up across the whole chapter, and it is worth seeing the chain end to end: the ECMU's ADIRU input (see ECMU) → the 2PC/3PC closing condition (see DC Network Transfer) → the static inverter's three activation cases (see Static Inverter) → the two distribution-table rows (see the overview). The instant the landing roll decelerates through 50 kt, the supply face automatically widens by one notch.

The discharge horn (ground only): external-power contactor off + generators not turning + BAT at AUTO and connected → an external horn sounds, stopping automatically after 5 minutes (see Batteries and the BCL). It is not a fault warning — it is a ground-service reminder that "the aircraft is eating the battery".

3. The degradation ladder — a full recap

This is the chapter's whole failure face on one page — the overview ladder, now filled in with the detail of articles 21–29:

Two things to read out of the ladder. First, each rung down, the "automatic" share shrinks and "your" share grows — at rung 5 the system has no cards left, and time is charge. Second, the ladder is not walked rung by rung: a red-line fault (the 1' class — overcurrent / GLCF / IPT) jumps straight past "borrow" to "lose a bus", and EMER CONFIG can arrive in one stroke. The ladder is a map of where you can be, not a sequence you descend one step at a time.

4. Flight-deck scenarios

1. After RAT-scenario slats extension (= entering this configuration). The screens shrinking one more notch is expected (see EMER CONFIG); check three things — PFD 1 present, VHF 1 present, the battery voltmeter (select 1/2) reading > 25 V; then continue the approach and do not chase restoration (the slats-retract MAN ON revival is the go-around scenario — see Emergency Generator).
2. Charge-management thinking. The source library gives no "how many minutes" figure — a transparent boundary, not an omission to be filled by extrapolation. Your only two levers are reduce load (do not switch on the unnecessary) and reduce time (shortest track, land first time). The voltage trend carries more information than the absolute value: a steady fall means load exceeds battery capability.
3. Landing roll through 50 kt. Activation passes to the BAT pb (the static inverter's third case) — keep both at AUTO, do not touch; after stopping, switch off the batteries as required (the horn will remind the ground that the aircraft is still eating the battery).

[!warning]- Common misconceptions — predict, then check

Read each statement, decide true or false, then check the truth in brackets.

1. "On batteries only, the LAND RECOVERY buses need the pushbutton pressed to be supplied." — False. They are supplied whatever the LAND RECOVERY pb position (407PP permanently supplied); the FCOM states this directly.
2. "The battery will last a known number of minutes." — False / not given. The source library (FCOM / QRH / AMM) gives no endurance figure; manage by trend (reduce load, reduce time), do not extrapolate a number.
3. "The degradation ladder is always walked one rung at a time." — False. A red-line fault (overcurrent / GLCF / IPT) skips straight from rung 1 past the borrow to a lost bus; EMER CONFIG can arrive in one stroke. The ladder is a map, not a forced sequence.

Self-test

[!note]- Q1. On batteries only in flight, which buses still have power, and why is the SHED family entirely gone?

The batteries supply DC ESS BUS + DC LAND RECOVERY (whatever the pb), and through the static inverter AC ESS BUS + AC LAND RECOVERY (whatever the pb); AC ESS SHED / DC ESS SHED / SHED LAND RECOVERY are not supplied, and AC ESS GND is lost. The SHED family is gone because the 2.5 kVA static-inverter budget only covers the ESS core. The DC BAT BUS is held only 7 s.

[!note]- Q2. What differs on either side of the ground 50 kt split?

On the ground at ≤ 50 kt (both BAT at AUTO), the batteries also gain DC BAT BUS (3PP fed directly) and AC ESS GND (905XPB, ground-only). The 50 kt boundary is the unified ECMU(ADIRU) → 2PC/3PC → static-inverter line; through 50 kt on the roll the supply widens by one notch.

[!note]- Q3. What are the three conditions for the discharge horn?

External-power contactor off + generators not turning + BAT at AUTO and connected → an external horn sounds, stopping automatically after 5 min — a ground-service reminder, not a fault warning.

[!note]- Q4. What does the 1' rung of the ladder mean?

The red-line protections (overcurrent / GLCF / IPT trip) lock the BTC and do not reconfigure — the ladder skips the "borrow" step and goes straight to "one AC BUS lost" (the AC BUS FAULT procedure). The ladder is not necessarily descended rung by rung: red-line faults jump levels.

[!note]- Q5. What instruments and charge management are left in this configuration?

PFD 1 / ISIS / VHF 1 / the battery voltmeter (the all-black master instrument, > 25 V red line); the two management levers are reduce load + reduce time; the voltage trend matters more than the absolute value; the endurance figure is not given by the source library (do not extrapolate).

Key takeaways

References

Per FCOM DSC-24-10-30-30 (the flight and ground batteries-only segments, the identical-ECAM-page note, the discharge horn) and DSC-24-10-30-40 (the distribution table, the 7 s footnote, the 50 kt rows); the degradation-ladder recap is an integrative synthesis of the verified facts of articles 21–29 (cross-linked to overview, Emergency Generator, Batteries and the BCL, Static Inverter, EMER CONFIG). The endurance ("how many minutes") figure is not in the source library and is not extrapolated. This is a synthesis article with no new mechanism, and carries no separate MEL section.

Independent study material, not an Airbus publication. Refer to current operator FCOM, FCTM, and QRH for operational use.