Climbing and Descending — Theory Part 2: Descending

Climbing and Descending — Theory Part 2:

Descending

CASA Recreational Pilot License (Aeroplane) — Lesson 3, Pre-flight theory

All text and presenter notes in this briefing are licensed under Creative Commons BY-SA 4.0. More info

Climbing and Descending — Theory Part 2: Descending

Theory Overview — Part 2

Climbing and Descending — Theory Part 2: Descending

Learning Objectives — Descending

By the end of this session, our aim is to be able to:

  • Describe how we manipulate the four forces to produce a descent
  • Apply the performance formula at both the descent entry and descent exit
  • Name three types of descents and when to use each
  • Describe best glide speed and the factors that affect glide range

...so that we can experience and practise descents in our flight later.

Climbing and Descending — Theory Part 2: Descending

Forces in the Descent

Climbing and Descending — Theory Part 2: Descending

Aerodynamic forces — descending

In a descent, thrust is less than drag:

  • The weight component along the flight path now acts forward — replacing the missing thrust
  • The aeroplane trades altitude for airspeed to maintain flying speed
  • The steeper the descent, the larger the weight component pulling the plane forward.

In a glide, the weight component forward balances drag — the aeroplane flies at a steady speed with no thrust at all.

Climbing and Descending — Theory Part 2: Descending

The performance formula in a descent

The performance formula still applies — same as the climb:

Power + Attitude = Performance

For a descent:

  • Set low power (reduced, or idle for glide)
  • Set a nose-down attitude (nose below the horizon)
  • Performance — the aeroplane descends at the expected airspeed

The pilot selects the power and attitude; the airspeed follows — same principle as the climb, different direction. Never chase the airspeed with the controls — set the attitude and wait for the speed to stabilise.

Climbing and Descending — Theory Part 2: Descending

Descent Entry and Exit

Climbing and Descending — Theory Part 2: Descending

Descent entry — Power, Attitude then Trim

Descent entry — PAT:

  1. Power — reduce to descent power (or idle for glide)
  2. Attitude — hold level briefly until airspeed reduces to the anticipated speed for the descent, then lower nose to descent attitude
  3. Trim — trim off any forward pressure; hands off

Maintaining the descent — ALAP work cycle:

  • Attitude — is the nose position correct relative to horizon?
  • Lookout — traffic scan
  • Attitude — confirm the nose still on attitude
  • Performance — quick glance inside: RPM, airspeed, altimeter as expected?
Climbing and Descending — Theory Part 2: Descending

Levelling out from descent — PAT

Anticipate leveling out around 50–100 ft before your target altitude (or 10% of your rate of descent)

  1. Power — apply cruise power
  2. Attitude — raise nose to level-flight attitude
  3. Trim — trim for hands-off

Both descent entry and level-off use PAT — unlike the climb level-off (APT), power goes in first to arrest the descent before raising the nose.

Climbing and Descending — Theory Part 2: Descending

Types of Descent

Climbing and Descending — Theory Part 2: Descending

Three types of descent

The handbook for your training aeroplane (and your instructor) will give you the power settings and speeds for each type of descent. As an example, the Piper Warrior 151, targeting a descent rate of around 500 ft/min:

Descent type Power Speed Best used for
Cruise descent 2200 RPM 90 KIAS Normal descent from cruise; comfortable; easy to level off
Best range glide Idle 73 KIAS (best glide) Maximum distance from altitude with engine failure
Approach descent 1700 RPM, 2 stages of flap 70 KIAS Circuit and landing; uses flap
  • Cruise descent — small power reduction, gentle nose-down; airspeed similar to cruise
  • Glide — engine at idle; nose attitude set for best glide speed; maximum range
  • Approach — power and attitude adjusted together; flap increases drag to steepen the path
Climbing and Descending — Theory Part 2: Descending

Glide — best range descent

A glide is a descent with power at idle. The aeroplane trades altitude for distance.

  • Best glide speed — published in your aeroplane's handbook (e.g. 73 KIAS for the Warrior 151) — gives the maximum distance per foot of altitude lost
  • Too slow: induced drag increases; glide range decreases
  • Too fast: parasite drag increases; glide range also decreases
  • There is one optimal speed — not "as slow as possible"

Factors affecting glide range:

  • Flaps extended — increase drag, shorten glide; retract for maximum range
  • Weight — heavier aircraft glides at a higher best glide speed but the same glide angle
  • Headwind — reduces range over the ground; tailwind increases it
Climbing and Descending — Theory Part 2: Descending

Approach descent with flap

For an approach descent, flap increases drag and steepens the path without increasing airspeed:

  • Flap extension lowers the nose — re-trim after each stage
  • Power controls rate of descent — more power → shallower; less power → steeper
  • Attitude controls airspeed — raise nose → slower; lower nose → faster

This is the reversal from straight and level — in the approach:

Power = altitude (rate of descent). Attitude = airspeed.

Standard approach descent sequence:

  1. Reduce to approach power
  2. Extend flap first stage — note pitch change, re-trim
  3. Adjust attitude for target approach speed
  4. Add further flap stages as required
Climbing and Descending — Theory Part 2: Descending

Instrument Indications

Climbing and Descending — Theory Part 2: Descending

What the instruments show during climbs and descents

Instrument In a climb In a descent
Airspeed indicator Settles at climb speed (VY, VX, or cruise) Settles at descent/glide speed
Altimeter Steadily increasing Steadily decreasing
Vertical speed indicator Positive (up); lags slightly Negative (down); lags slightly
Engine gauges Watch CHT/OAT — prolonged climb works engine harder Temperatures may drop on extended glide

The vertical speed indicator lags — it shows the trend, not the instantaneous rate. Fly the attitude; use instruments to cross-check.

Climbing and Descending — Theory Part 2: Descending

Recap

Climbing and Descending — Theory Part 2: Descending

Part 2 Recap — Descending

Can you answer each of these?

  • What forces change in a descent compared to straight and level?
  • What is the descent entry sequence? What about the level-off — and why does PAT apply to both?
  • Name the three types of descent and when you would use each
  • What is best glide speed, and why is there an optimal speed (not just "fly slowly")?
  • In an approach descent, what does power control? What does attitude control?
  • What will the VSI show during a steady descent? Does it respond instantly?
Climbing and Descending — Theory Part 2: Descending

Arrival

Part 2 builds on the climb session. The same performance formula applies — we just change the power and attitude inputs to produce a descent rather than a climb. Introduce the three types of descent with the same pattern used for the three types of climb.

Mirror the structure from Part 1 where possible — students find it easier to learn new content that follows a familiar pattern.

Return to these at the recap. Ask the student to answer each from memory before revealing.

Click Direct-To to advance to Forces in the Descent.

Key concept: the energy exchange in a glide — the aeroplane is converting potential energy (altitude) into kinetic energy (airspeed) to overcome drag. This is why best glide speed is not "as slow as possible". **Actions** - Reduce power from 60 to 50% and watch thrust reduce while drag stays - Reduce attitude from 4 to 1.5 and watch drag increase - Reduce the attitude to -8 degrees to show the components of the weight contributing to: - Forward speed - Balancing the lift - **Still in balance** - not accelerating down or forward, just constant speed.

Reinforce the symmetry with the climb: the formula doesn't change, only the inputs. This is the core of attitude flying.

Click Direct-To to advance to Descent Entry and Exit.

PAT gets you into the descent; ALAP keeps you there. Same work cycle as the climb — three steps outside, one quick glance inside.

The contrast with the climb level-off (APT) is worth highlighting. In a descent, adding power first arrests the sink rate; then the attitude is raised to level. If you raise the nose first without adding power, the airspeed bleeds off rapidly.

Click Direct-To to advance to Types of Descent.

The table values are Warrior 151 examples — check the equivalent power settings and speeds for your training aeroplane before the lesson. Mirror the three-types pattern from Part 1. Students can now see the parallel: three types of climb, three types of descent, each with its own use case.

Know the best glide speed and approximate glide ratio for your training aeroplane — for the Warrior 151 that's approximately 73 KIAS at max gross weight and a 10:1 glide ratio (for every 1000 ft, approximately 1.7 nm of range). This is a critical airspeed to know — it will come up again in the engine failure forced landing lesson.

The "power = rate of descent, attitude = airspeed" rule is counterintuitive at first. Use this as a preview — they will practise it in earnest during circuits. Don't dwell too long here.

Click Direct-To to advance to Instrument Indications.

Emphasise that the instruments confirm what the attitude is producing — don't fly the VSI. The primary reference is always the nose position relative to the horizon.

Click Direct-To to advance to the recap.

Ask one at a time. End the session positively. The student now has the full picture for climbing and descending — ready to take it to the aeroplane in the flight brief.