Don Bateman, the Enhanced Ground Proximity Warning System, and the Cockpit Alarm That Turned Controlled Flight Into Terrain from an Epidemic into a Near-Extinct Accident Category

Controlled flight into terrain - CFIT - was the leading cause of fatal airline accidents through the 1960s and into the 1970s. Don Bateman, an engineer at Sundstrand Data Control in Redmond, Washington, changed that by recognizing that all the data needed to prevent these accidents was already on the airplane. The warning system he developed, later enhanced with GPS and a worldwide terrain database, reduced CFIT in equipped commercial aircraft by roughly 90 percent compared to the pre-GPWS baseline.

What Made CFIT So Deadly

Through the late 1960s and early 1970s, there were roughly three to five fatal CFIT accidents per year in commercial aviation worldwide. These were not accidents caused by mechanical failure or extreme weather. They involved airworthy aircraft flown by qualified crews who simply did not know terrain was in their path.

The pattern was consistent: high ground at night, rising terrain in poor visibility, a crew distracted by a minor instrument indication while the terrain closed in quietly. CFIT was not an outlier in the accident statistics of that era - it was the number one cause of fatalities in a generation of airline travel.

The Data Was Already on the Airplane

What makes this story compelling from an engineering standpoint is that the information needed to prevent most of those accidents already existed in the cockpit. Every transport-category aircraft had a radio altimeter measuring actual height above the surface. Every aircraft had airspeed data, gear and flap position information, and glide slope deviation from the Instrument Landing System.

The raw data existed. No one had built the box that looked at all of it together and recognized the pattern.

How Don Bateman Built the Solution

Bateman’s position at Sundstrand - a company that manufactured flight data recorders - gave him years of access to post-accident data. What he kept seeing was not randomness. Specific combinations of instrument readings appeared consistently in the final seconds before CFIT events:

High descent rate at low altitude
Gear up at low altitude with high power
Gear up and flaps up below a certain radar altitude
Excessive deviation below the ILS glide slope

His core insight: if these parameter combinations appeared in accident data, they would also appear in real time on a flying aircraft before the accident happened. The signatures could be monitored continuously, and a warning could be triggered the moment the combination appeared - giving the crew time to react.

The Five Modes of the Original GPWS

The FAA mandated the Ground Proximity Warning System (GPWS) for Part 121 air carriers in 1974. The original system monitored five warning modes, each drawn directly from accident records.

Mode 1 - Excessive descent rate: If the rate of descent was too high relative to radio altitude, the system triggered. Sink rate. Pull up.

Mode 2 - Excessive closure rate to terrain: This addressed rising terrain beneath a level aircraft. Radio altimeter readings dropping too fast relative to airspeed meant the ground was coming up - not that the aircraft was descending into it.

Mode 3 - Altitude loss after takeoff or go-around: A sudden loss of altitude during climb-out required immediate crew awareness.

Mode 4 - Insufficient terrain clearance with incorrect configuration: Too low with gear or flaps in the wrong position for the phase of flight. Too low, gear. Too low, terrain.

Mode 5 - Excessive ILS glide slope deviation: Below glide slope at low altitude is precisely the scenario that puts aircraft into terrain short of the runway threshold.

Five modes. Five parameter signatures pulled from accident records. The system listened to instruments already on the airplane, evaluated the combinations, and spoke to the crew.

Why the System’s Specificity Was Intentional

The original GPWS was not designed to be broadly sensitive. It was designed to be highly specific. False alarms are operationally catastrophic in aviation - if a warning system activates on every other approach, crews begin to discount it. Bateman understood this. When the original GPWS activated, it meant something specific, and that design discipline was central to the system’s effectiveness.

The Limitation the Original System Could Not Address

After GPWS became mandatory and fleets began retrofitting it, CFIT accidents in equipped aircraft dropped substantially. But cases persisted - and they exposed a fundamental limitation.

The original system was reactive. It measured what was directly below the aircraft and what the aircraft was currently doing at that moment. It could not look ahead. If a crew was on a stabilized approach at the correct descent rate, in the correct configuration, headed toward a mountainside simply in their path, the original GPWS was silent. It had no terrain database. It had no position data. It only knew what was below and what the aircraft was doing right now.

That limitation continued to show up in accidents involving approaches into mountainous terrain and visual approaches in marginal conditions.

EGPWS: Adding Forward-Looking Terrain Awareness

By the mid-1990s, AlliedSignal - which had acquired Sundstrand - combined the original GPWS logic with a worldwide terrain database and GPS position information. The result was the Enhanced Ground Proximity Warning System, EGPWS.

Now the system knew not just what was below, but what was ahead. The aircraft’s computed position, altitude, and projected flight path were compared against the terrain database continuously. If the projected path intersected terrain within a warning threshold, the system spoke up before the aircraft reached it - potentially two to three minutes ahead of the projected impact point.

The cockpit terrain display - green, yellow, and red coding on glass cockpit screens - gave crews a visual picture of terrain, not just reactive audio warnings. EGPWS also incorporated windshear detection using the same data-fusion approach, correlating groundspeed, airspeed, and inertial data.

AlliedSignal merged with Honeywell in the late 1990s, and Honeywell’s EGPWS became the dominant system in the market. The International Civil Aviation Organization (ICAO) adopted Terrain Awareness and Warning System (TAWS) as the generic regulatory term and mandated it for turbine-powered transport aircraft in the early 2000s.

The Impact on the Accident Record

The effect is not subtle. Industry and regulatory studies from the late 2000s showed reductions in the range of 90 percent for CFIT accidents in aircraft equipped with functioning TAWS, compared to the pre-EGPWS baseline. The accident category that had been the number one cause of airline fatalities for a generation became a rare event in the equipped fleet.

Don Bateman received the Collier Trophy for his work on EGPWS. Previous recipients include the Wright Brothers, Chuck Yeager, and the Apollo program teams. The fact that the award went to Bateman for a warning box reflects the magnitude of the problem he solved.

What This Means for General Aviation Pilots

The TAWS mandate applies to turbine aircraft above certain weight thresholds operating under Part 125 and Part 121. It does not apply to piston singles, light twins, or most general aviation aircraft operating under Part 91. CFIT remains a leading cause of fatal accidents in general aviation to this day.

The technology is now accessible to GA pilots in ways it was not a generation ago. Terrain warning capability is built into the Garmin GTN series, G1000, and G3X platforms. ForeFlight and the Garmin Pilot app both integrate terrain alerting overlays. If you fly with a modern Garmin panel, you likely have some version of terrain depiction available.

Understanding What Your Terrain System Can and Cannot Do

Having terrain depiction on a moving map is not the same as understanding its design boundaries.

The terrain database requires accurate GPS position to function correctly. The alerting logic is calibrated for typical approach profiles. Flying an unusual trajectory or operating at an airport with a non-standard approach path means understanding the system’s assumptions before relying on its silence as confirmation of terrain clearance.

Alert fatigue is real. In mountainous terrain, continuous yellow depictions can blend into background noise. The pilots who get the most value from these systems read the display deliberately rather than glancing at it. The color coding communicates something specific: green means adequate clearance, yellow means pay attention, red means act now.

These systems were designed to interrupt you at the moment the data says you need to be interrupted. They are not wallpaper.

CFIT did not go away in commercial aviation because pilots got better. Pilots in 1972 were not less skilled than pilots today. It went away because someone built a box that made the terrain visible and audible at a moment when the crew still had options - not replacing pilot judgment, but giving pilots information they could not otherwise have.

Key Takeaways

CFIT was the leading cause of fatal airline accidents through the late 1960s and early 1970s, occurring roughly three to five times per year globally, with survivors in almost none of them.
Don Bateman at Sundstrand Data Control built the original GPWS by identifying repeating parameter signatures in accident data and recognizing those same signatures would appear in real time before a future accident.
The FAA mandated GPWS for Part 121 carriers in 1974; ICAO mandated TAWS for turbine transport aircraft in the early 2000s, and industry studies showed roughly a 90 percent reduction in CFIT for equipped aircraft.
EGPWS added forward-looking capability using GPS and a worldwide terrain database, warning crews up to two to three minutes before projected terrain contact - something the original reactive system could not do.
CFIT remains a leading cause of GA fatal accidents. Terrain display technology is widely available in modern GA avionics, but effectiveness depends on understanding what the system can and cannot do - and reading the display with intent, not habit.