TAWSTerrain Awareness and Warning System

TAWS — Terrain Awareness and Warning System

Technology · terrain-and-collision-avoidance · FAA TSO-C151c

TAWSAcronym

Terrain Avoidance and Warning SystemAlso known as

Definition

TAWS (Terrain Awareness and Warning System) is the FAA/ICAO regulatory term for onboard systems that use GPS position and a terrain and obstacle database to warn pilots of hazardous proximity to terrain. In current practice it is fulfilled by Enhanced Ground Proximity Warning System (EGPWS) equipment, so the two terms are now used almost interchangeably.

Overview

TAWS is a class of avionics that continuously compares an aircraft's position, altitude, and flight path against terrain and obstacle data to alert pilots before a Controlled Flight Into Terrain (CFIT) accident can occur. "TAWS" is primarily a regulatory and performance designation; the underlying technology that satisfies it is the Enhanced Ground Proximity Warning System.

How TAWS Relates to GPWS and EGPWS

TAWS did not replace GPWS so much as formalize the requirement that GPWS-family equipment evolved to meet:

**GPWS**, developed in the late 1960s, relies on radio-altimeter closure-rate data to warn of excessive descent rates or sudden ground proximity. It cannot "see" terrain that rises steeply ahead of the aircraft, which limits its warning time in mountainous or fast-rising terrain.

**EGPWS**, introduced in the 1990s, added GPS positioning and a worldwide digital terrain and obstacle database, enabling forward-looking terrain avoidance alerting and a graphical terrain display - the features that address GPWS's main weakness.

**TAWS** is the name the FAA (from its March 2000 rule) and ICAO gave to the performance standard that EGPWS-class equipment must meet to be installed on covered aircraft. In everyday and technical use today, "TAWS" and "EGPWS" describe essentially the same equipment: EGPWS is the technology, TAWS is the regulatory requirement it satisfies, and plain "GPWS" now refers to the earlier, superseded generation. See the portal's GPWS entry for the underlying alerting technology and its history.

Class A and Class B

FAA Technical Standard Order TSO-C151 defines two TAWS equipment classes:

**Class A**: required for Part 121 airline operations and larger Part 135 aircraft (10 or more passenger seats); must include a terrain/obstacle situational display plus the full set of alerting modes, including forward-looking terrain avoidance and premature descent alerting.

**Class B**: required for turbine-powered aircraft with 6-9 passenger seats under Parts 91/135; provides the core alerting modes (excessive descent rate, terrain closure rate, altitude loss after takeoff, and others) without a mandatory terrain display.

Regulatory Basis

**FAA**: 14 CFR 91.223, 121.354, and 135.154 require an approved TAWS meeting TSO-C151 on U.S.-registered, turbine-powered airplanes with six or more passenger seats, phased in between 2002 and 2005.

**ICAO**: Annex 6 mandates terrain awareness warning system carriage by aircraft category.

**EASA**: the equivalent European requirement is set out in CAT.IDE.A.150.

Why It Matters

By adding GPS position and a terrain database to the radio-altimeter-only logic of classic GPWS, TAWS/EGPWS gives crews substantially earlier and more reliable terrain warnings, and it is widely credited with sharply reducing CFIT accidents, historically one of commercial aviation's leading causes of fatal accidents.

Related Terms

Standards & References

✦FAA TSO-C151c

✦14 CFR 91.223

✦14 CFR 121.354

✦14 CFR 135.154

✦ICAO Annex 6

Sources

reference

Terrain Avoidance and Warning System (TAWS) ↗SKYbrary / EUROCONTROLAccessed: 2026-09-11

industry-organization

Terrain Awareness and Warning Systems (TAWS) and Ground Proximity Warning Systems (GPWS) ↗National Business Aviation Association (NBAA)Accessed: 2026-09-11

regulator

Terrain Awareness and Warning System (14 CFR 91.223 et al.), Federal Register ↗FAAAccessed: 2026-09-11

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Last verified: 2026-09-11 · Status: verified