in aviation, few instruments are as critical as the altimeter.
At first glance, its job seems simple:
- indicate altitude.
But in reality, an incorrect pressure setting or loss of vertical situational awareness can quickly initiate a catastrophic chain of events.
Throughout aviation history, several major accidents demonstrated how:
- altimeter setting errors
- faulty radio altimeters
- premature descents
- incorrect QNH settings
- loss of altitude awareness
became contributing factors in fatal crashes.
Many of these accidents helped reshape:
- IFR procedures
- CRM training
- TAWS/EGPWS systems
- cockpit automation philosophy
- vertical situational awareness
- modern aviation safety culture
The Altimeter Does Not Measure Altitude Directly
One of the first lessons in flight training is understanding that:
The altimeter is actually a pressure instrument.
It interprets atmospheric pressure and converts it into an altitude indication.
Because of this:
- incorrect QNH
- wrong standard pressure settings
- sensor failures
- or poor altitude awareness
can generate dangerous vertical errors.
Under IFR conditions, at night, or in mountainous terrain, those errors can become fatal.
American Airlines Flight 1572
Incorrect Altimeter Setting During Approach
American Airlines Flight 1572
In November 1995, an American Airlines Boeing 757 was approaching Bradley International Airport in poor weather conditions.
During the approach, the aircraft struck trees and approach lighting equipment before reaching the runway.
Investigators identified:
- incorrect altimeter setting
- descent below glide path
- reduced situational awareness
The altimeter had been improperly adjusted, creating a significant altitude indication error.
The accident reinforced the importance of:
- crew cross-check procedures
- IFR discipline
- constant altitude awareness
Turkish Airlines Flight 1951
Faulty Radio Altimeter and Automation Dependency
Turkish Airlines Flight 1951
The crash of the Turkish Airlines Boeing 737 near Amsterdam became one of aviation’s most important cases involving:
radio altimeter failure.
The defective sensor falsely indicated incorrect altitude close to the ground.
As a result:
- the autothrottle reduced engine power prematurely
- airspeed decayed
- the aircraft stalled
- and crashed short of the runway
The accident exposed the risks of:
- excessive reliance on automation
- trusting faulty altitude data
- inadequate crew monitoring
After the crash, important Boeing operational changes were introduced.
American Airlines Flight 965
Loss of Vertical Situational Awareness
American Airlines Flight 965
The crash near Cali, Colombia became one of the most studied CFIT accidents in aviation history.
Although navigation and FMS management were primary issues, investigators also identified:
- loss of vertical awareness
- confusion regarding terrain and descent profile
- poor altitude management
The aircraft ultimately impacted mountainous terrain during a nighttime approach.
The accident accelerated improvements in:
- CFIT training
- terrain awareness systems
- situational awareness procedures
Air New Zealand Flight 901
Altitude Misjudgment in Whiteout Conditions
Air New Zealand Flight 901
The 1979 Air New Zealand accident in Antarctica also involved factors related to altitude perception and situational awareness.
The crew believed the aircraft was in a safe position when it collided with Mount Erebus.
The accident demonstrated how:
- navigation
- visual references
- altitude perception
- and “whiteout” weather conditions
can completely deceive even highly experienced crews.
The Danger of CFIT
Many of these accidents fall under the category of:
CFIT — Controlled Flight Into Terrain
This occurs when:
- the aircraft is fully controllable
- engines are functioning
- systems are operational
but the crew loses situational awareness and unintentionally flies into terrain.
For decades, CFIT was one of the leading causes of fatalities in commercial aviation.
How These Accidents Changed Aviation
These tragedies led to major improvements in:
- TAWS/EGPWS systems
- CRM
- altitude callouts
- sensor redundancy
- automation management
- cross-check procedures
- terrain awareness training
Modern pilots are now trained extensively to:
- verify QNH
- cross-check altimeters
- monitor minimum altitudes
- confirm transition levels
- avoid automation complacency
A Small Error Can Become a Major Disaster
A seemingly minor pressure-setting mistake can generate hundreds of feet of altitude deviation.
During IFR approaches, mountainous operations, or low-visibility conditions, that can be enough to trigger a fatal accident.
That is why cockpit phrases such as:
- “QNH checked”
- “Standard set”
- “Cross-check altimeters”
carry enormous operational importance.
Final Thoughts
Accidents involving altimeter errors profoundly changed modern aviation safety culture.
They demonstrated that:
- instruments must be fully understood
- automation must always be monitored
- situational awareness is critical
- and small technical details can save lives
In aviation, altitude is never “just a number.”
It represents separation, awareness, and survival.
Marcuss Silva Reis
Commercial Pilot – Airplane
Professor of Aeronautical Sciences
Aviation Safety Expert and Aviation Consultant
Editor – Instituto do Ar Aviation Blog
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