Description

Terrain awareness implies an appreciation of the nature of the terrain over which an aircraft is flying, with particular reference to high and low ground and obstacles.

Flight Safety Foundation (FSF) Approach-and-landing Accident Reduction (ALAR) Briefing Note 5.2 — Terrain defines terrain awareness as:

"the combined awareness and knowledge of the following:

• Aircraft position
• Aircraft altitude
• Applicable minimum safe altitude
• Terrain location and features, and
• Other hazards."

The briefing note asserts that, "Navigation deviations and inadequate terrain separation are usually the results of monitoring errors."

"Monitoring errors involve the crew’s failure to adequately monitor the aircraft trajectory and instruments while programming the autopilot or flight management system (FMS), or while being interrupted or distracted."

Effects

Lack of terrain awareness can result in dangerous proximity to, or collision with, the ground or an obstacle (CFIT).

Defences

• Pre-flight and pre-descent briefing using suitable maps improves terrain awareness;
• GPWS or TAWS is the most effective defence against CFIT accidents.
• Provision by States of Electronic Terrain and Obstacle Data (eTOD).

Typical Scenario

An aircraft is approaching an airfield by night in good VMC. The pilot has the runway in sight, cancels IFR and commences a visual approach. Due to lack of terrain awareness, the aircraft strikes high ground on the approach to the runway.

Contributory Factors

• Darkness
• Visibility
• Weather or Low cloud
• Complacency

Solutions

According to the briefing note, "Terrain-awareness elements of effective cross-check and backup include:

• Assertive challenging
• Altitude calls
• Excessive parameter-deviation calls; and,
• Task-sharing and standard calls for the acquisition of visual references.

"Terrain awareness can be improved by correct use of the radio altimeter. The barometric-altimeter bug and the radio altimeter decision height (RA DH) bug must be set according to the aircraft manufacturer’s SOPs or the company’s SOPs."

An important element of monitoring is ensuring that the correct altimeter pressure setting is set.

The States are required by ICAO Annex 15 (Chapter 10) to provide electronic terrain and obstacle data (eTOD) for the use in different air navigation applications including GPWS, MSAW, flight simulators, electronic charts etc.

Related Articles

• Situational Awareness
• Somatogravic and Somatogyral Illusions
• Terrain Avoidance and Warning System (TAWS)
• Use of Radio Altimeter
• Night Visual Approaches

Further Reading

Flight Safety Foundation

• ALAR Briefing Note 5.2 — Terrain

The Flight Safety Foundation ALAR Toolkit provides useful training information and guides to best practice. Copies of the FSF ALAR Toolkit may be ordered from the Flight Safety Foundation ALAR website Flight Safety Foundation ALAR website

Airbus Operational Environment Briefing Notes

• Enhancing Terrain Awareness

Terrain and Obstacle data

• ICAO Annex 15 Chapter 10 Terrain and Obstacle Data, Appendix 8 Numerical requirements for Terrain and obstacle data
• EUROCONTROL Terrain and Obstacle Manual, November 2015