Skip to content
PilotSchool Knowledge Base

Revising Estimates and ETA Calculations

Introduction

Effective navigation is crucial for pilots to ensure safety and efficiency. This section covers essential in-flight navigation skills for revising or confirming estimates of arrival times (ETAs), using map plotters, and employing mental dead reckoning techniques such as the 1-in-60 rule. These skills are vital for the CASA PPL pilot license and involve real-time adjustments and problem-solving under varying conditions.

Revising or Confirming ETA Using Latest Groundspeed

Overview

Revising or confirming the Estimated Time of Arrival (ETA) is a critical in-flight procedure, requiring adjustments based on real-time variables like wind changes. This ensures the flight path remains safe and efficient.

Groundspeed Calculations

  • 6-Minute Markers Technique: Calculate groundspeed using:

    For example, covering 8 nautical miles in 6 minutes corresponds to a groundspeed of 80 knots. Practical Flying Guide 1 - CAA and Avsec

  • E6B Flight Computer: This is used to calculate true course, wind correction, groundspeed, and ETA. If the groundspeed is 91 knots over 57 nautical miles, the ETA can be calculated at 39 minutes. AeroGuard Flight Training Center

Adjusting ETA

Using proportional techniques, adjust ETA based on elapsed time discrepancies. A one-minute delay at one-third of a leg suggests adding two minutes for the remaining journey.
Practical Flying Guide 1 - CAA and Avsec

Mental Dead Reckoning and Map Plotter Usage

Map Plotter Functionality

Navigational plotters help determine true course and measure distances:

  • Align the plotter’s protractor with a map meridian and course line.
  • Measure distances using the nautical mile scale on the plotter’s ruler.

Source: Navigational Plotter Instructions - Gleim Aviation

Mental Dead Reckoning Techniques

1-in-60 Rule

A fundamental navigation principle allows for quick mental calculation of drift and corrections during flight:

  • Formula: If 1 nautical mile off after 60 miles, the drift angle is (1^\circ).
  • General use:

Example: Deviating 3 miles left after 20 miles of a 50-mile flight requires a 9-degree adjustment right to correct the track.

Source: NZ Aviator

Clock System for Drift Calculation

Convert drift angles into clock face fractions for crosswind components:

  • Calculate maximum drift = (\text{Wind Speed} / \text{TAS}).
  • Use clock fractions (e.g., 15° = 1/4).

Source: British Aerobatic Academy

Estimating Track Required (TR) and Estimated Time Interval (ETI) to Diversion Points

Key Concepts

Mental calculations are essential when determining TR and ETI for diversions:

  • Time, Speed, and Distance Basics:
    • Convert speed in knots for calculating time and distance.
    • Example: 60 knots implies 1 nautical mile/minute.

Example of Diversion Scenario:

  • Calculate required TR and ETI with known discrepancies and diversion requirements.

Sources:

Practical Implications

Understanding these techniques enhances a pilot’s ability to adapt quickly and manage challenges like unscheduled diversions due to various influences such as weather or operational constraints.

This section provided an integrated view of fundamental navigation skills, using tools like the E6B, map plotters, mental techniques like the 1-in-60 rule, and adopting a structured approach for solving in-flight navigation problems. Mastery of these concepts is instrumental for any pilot seeking a CASA PPL license.