Navigation (CNAV)

True, Magnetic & Compass Direction

The difference between true and magnetic north, applying magnetic variation, and correcting for compass deviation.

• CASR Part 61 MOS Schedule 3 (NV) 2.1.1 (p.493) — Form of the earth — true versus magnetic north, variation and deviationVerified“Explain the following terms listed in (a) to (g): (a) the shape and rotation of the earth; and (b) latitude, longitude; and (c) equator, Greenwich meridian; and (d) great circles, small circles, rhumb lines; and (e) difference between true and magnetic north; and (f) terrestrial magnetism, magnetic variation and the change in variation with time; and (g) distance on the earth.”
• CASR Part 61 MOS Schedule 3 (NV) 2.4.2 (p.490) — Applying magnetic variation to obtain magnetic directionVerified“Apply magnetic variation to obtain magnetic direction.”

• Variation EAST → magnetic LEAST. Variation WEST → magnetic BEST.
• That mnemonic runs TRUE → MAGNETIC. Reverse it going magnetic → true.
• Variation is caused by the earth; deviation is caused by the aircraft itself.
• The track over the ground does not change when you change reference north — only the number does.

Try the interactive animation for this topic in the app →

1-in-60 Rule & In-Flight Track Corrections

Calculating Track Error (TE), Closing Angle (CA), and total heading alterations to parallel or intercept destination.

• CASR Part 61 MOS Schedule 3 (NV) 2.5.3 (p.491) — Determining Track Made Good (TMG), drift and heading alterationsVerified“With reference to a planned or given track and given appropriate data: (a) determine track made good (TMG); and (b) calculate drift; and (c) determine alteration of heading or HDG(M) to: (i) parallel track; and (ii) intercept track at a nominated point; and (iii) maintain track once track is intercepted.”

• To fly PARALLEL to track: alter heading by Track Error (TE) only.
• To reach DESTINATION: alter heading by Track Error + Closing Angle (TE + CA).
• Track Error uses Distance FLOWN; Closing Angle uses Distance TO GO.
• Watch left vs right: if you are left of track, you must turn RIGHT to correct.

Try the interactive animation for this topic in the app →

Point of No Return (PNR) & Equi-Time Point (ETP)

Critical Point (ETP) balance between continuing vs returning, PNR safe fuel radius, and the effect of headwind/tailwind.

• CASR Part 61 MOS Schedule 3 (FP) 2.1.1 (p.541) — Practical flight planning exercise — critical point and point of no returnVerified“Complete a practical flight planning exercise using specified initial conditions and operations manual data. The exercise is intended as a consolidated test of a candidate’s ability to apply flight planning, performance and navigational principles, and will include calculating safe fuel endurance, critical point and point of no return.”

• Always use Groundspeed (GS), never Airspeed (TAS), in the ETP and PNR formulas.
• Headwind outbound moves ETP CLOSER TO DESTINATION (into the wind).
• Tailwind outbound moves ETP CLOSER TO DEPARTURE.
• Safe endurance must ALWAYS subtract mandatory fixed reserve (30/45 min) before computing PNR.

Try the interactive animation for this topic in the app →

Rotary-Wing Dead Reckoning

Low-level visual dead-reckoning navigation for helicopters: drift, heading to steer and groundspeed at typical rotary cruise speeds and low levels.

• CASR Part 61 MOS Schedule 3 (NV) 2.4.5 (p.491) — Calculating heading, groundspeed and driftVerified“Calculate the following: (a) CAS and TAS given air temperature and pressure height; (b) HDG, GS and drift given TAS, W/V, TR; (c) TR given HDG, TAS, W/V; (d) climb and descent rates and gradients; (e) TOPC and TOPD positions using average airspeed, W/V and rates of climb and descent.”

• The wind you plan with is not the wind you get at low level — surface friction backs and reduces it, so use the forecast area/low-level wind, not the 2,000 ft wind, for low-level legs.
• Helicopter cruise speeds are low, so a given wind produces a larger drift angle and a larger groundspeed change than in a faster aeroplane — aeroplane rules of thumb under-read it.
• Features pass quickly at low level; plan shorter legs and more frequent fixes than a light-aeroplane plan would use.
• Endurance is unforgiving at low groundspeed — a headwind eats time and fuel margin fast.

Rotary-Wing Fuel Requirements

Fuel planning for helicopter operations under CASR Part 91 / Part 133 — trip fuel, reserves and the fixed final reserve for piston vs turbine helicopters.

• CASR Part 61 MOS Schedule 3 (NV) 2.4.1 (p.494) — Solving fuel used / required / remaining / consumption problemsVerified“Review computations and conversions and: (a) solve GS, distance, fuel used, fuel required, fuel remaining and fuel consumption problems, given appropriate combinations of these factors; (b) solve CAS/TAS problems given air temperature and pressure height; (c) determine HDG, GS and drift.”
• CASR Part 91 MOS / CASR Part 133 Chapter 19 — Operating rule: fuel requirements (rotorcraft)Needs review

• Fixed final reserve for helicopters is a set time at holding speed, and it differs for piston versus turbine — it is not a percentage of trip fuel.
• Part 133 (air transport) fuel rules are stricter than Part 91 — check which one the question is set under before answering.
• Final reserve is planned to be untouched on landing; planning to arrive with exactly final reserve is planning to break the rule if anything goes wrong.
• Low groundspeed means holding and alternate fuel buy less distance and time than the same figures would in an aeroplane.

Navigation & Flight Planning — General

General visual navigation and flight planning: the triangle of velocities, dead reckoning, fuel and time calculations, and in-flight track keeping.

• CASR Part 61 MOS Schedule 3 — NavigationNeeds review

• Track is measured from true north on the chart; heading is what you fly after applying variation and deviation — do not compare the two numbers directly.
• Groundspeed, not airspeed, drives ETA and fuel — a headwind leg and a tailwind leg of equal distance do not average out in time.
• The 1-in-60 rule: track error uses distance flown, closing angle uses distance to go.
• Flight planning is in UTC — Australian time zones plus daylight saving are a common slip when converting to local.