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Lesson 8 · Flight Performance & Planning

Altimetry & Cruising Levels

QNH, QFE and standard; the transition layer; and the VFR semicircular rule — EASA PPL theory

⏱ ~20 min ✈ SEP · VFR 📋 EASA Part-FCL

1 — The Three Pressure Settings

An altimeter is just a barometer with a height scale. What it reads depends entirely on the reference pressure you dial into the subscale.

Three settings, three things the altimeter reads
Aerodrome Mean sea level (MSL) 1013 hPa standard datum QFE QNH QNE / 1013
QFE — reads height above the aerodrome
QNH — reads altitude above MSL
QNE / 1013 — reads pressure altitude → flight level
  • QNH — set it and the altimeter reads altitude above mean sea level; on the ground it shows aerodrome elevation. This is your normal VFR setting.
  • QFE — reads height above the aerodrome; it reads zero on that runway. Useful for circuits at some fields.
  • QNE / standard (1013.2 hPa, 29.92 inHg) — the common datum everyone shares up high, giving pressure altitude, read as a flight level (Lesson 1).

2 — Transition: Altitudes Below, Flight Levels Above

So that everyone at altitude shares one datum, aviation splits the vertical world in two at the transition altitude/level.

Transition altitude, transition level & the layer between
Flight levels — set 1013 Transition layer Altitudes — set QNH Transition level (TL) Transition altitude (TA) Descending: at the TL, set QNH Climbing: at the TA, set 1013

TA is published per State/aerodrome — e.g. Germany 5 000 ft, Austria 10 000 ft.

Below the transition altitude (TA) you fly altitudes on QNH. Above the transition level (TL) you fly flight levels on 1013. Between them sits the transition layer. The switch is one knob: climbing, set 1013 as you pass the TA; descending, reset QNH as you pass the TL.

TA is local, and published
The transition altitude is set per State or aerodrome, not universal — for example Germany 5 000 ft, Austria 10 000 ft (with local exceptions). Always use the published value; don’t assume.

3 — The Semicircular Cruising-Level Rule

In level cruise above 3 000 ft above the ground, you don’t pick any height you like — you fly a level appropriate to your magnetic track, so opposite-direction traffic is always separated by 1 000 ft. Drag the track and see:

Semicircular cruising levels — pick by magnetic track
N E S W
—

Applies in level cruise above 3 000 ft AGL. VFR levels are the IFR level + 500 ft.

Eastbound (track 000–179°): odd thousands + 500 ft → 3 500, 5 500, 7 500, 9 500 ft (FL35, 55, 75, 95). Westbound (track 180–359°): even thousands + 500 ft → 4 500, 6 500, 8 500 ft (FL45, 65, 85).

The shortcut
VFR levels are simply the IFR level + 500 ft. And the split is by magnetic track (where you’re going over the ground), not heading.

4 — “High to Low, Look Out Below”

Your altimeter only tells the truth if its setting matches the air around you. Fly from high pressure into lower pressure (or warm into colder air) without resetting, and the altimeter over-reads — you are lower than it shows.

High to low, look out below
Flying toward lower QNH on an old setting, the instrument reads higher than your true altitude — dangerous near terrain. Update QNH regularly from stations en route. The same trap applies flying into colder-than-ISA air.

5 — Worked Example & the Checks

You’re tracking 250° magnetic, below the TA, and want to cruise around 6 000 ft VFR:

  1. Setting: below the TA → QNH (you fly an altitude, not a flight level).
  2. Track band: 250° is 180–359° → westbound → even + 500.
  3. Level: the even-plus-500 option nearest 6 000 is 6 500 ft. (Eastbound, you’d have flown 5 500 or 7 500.)

Three quick checks
1. Below TA = altitude on QNH; above TL = flight level on 1013. 2. Above 3 000 ft AGL, level follows magnetic track (E odd+500, W even+500). 3. Keep QNH current — high to low, look out below.

Knowledge Check

Question 1
With QNH set, on the ground the altimeter reads:
Question 2
The standard pressure setting used for flight levels is:
Question 3
Climbing through the transition altitude, you should:
Question 4
Cruising VFR above 3 000 ft AGL on a magnetic track of 270°, near 6 000 ft, the correct level is:
Question 5
You fly toward an area of lower pressure but don’t update QNH. Your altimeter will:

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