Definition
A type of inertial navigation system in which the gyroscopes and accelerometers are mounted (strapped) directly to the airframe rather than on a mechanically gimballed stable platform. The sensors move with the aircraft, and a computer continuously calculates aircraft orientation and position by mathematically resolving the sensor outputs.
Plain English
An inertial navigation system whose motion sensors are bolted straight to the aircraft instead of sitting on a self-leveling platform. A computer does the work of figuring out which way is up and where the aircraft is going.
Context Anchor
Seen in instrument flying discussions about inertial navigation system components and how modern navigation equipment senses aircraft motion.
Derivation
The name describes the construction directly: the sensors are 'strapped down' to the airframe rather than isolated on a moving platform. The phrase highlights what makes this design different from earlier gimballed systems.
Why Pilots Care
Strapdown systems are lighter, more reliable, and require less maintenance than older gimbaled platforms while still providing accurate inertial data for navigation.
Grounding Statement
Picture the sensors riding firmly with the airplane while the computer works out what the airplane’s motion means.
Intuition Check
“Strap down” does not mean tying down cargo or securing the aircraft on the ramp. Here it means the navigation sensors are fixed to the aircraft structure and move with the aircraft.
Example Sentence 1
Most modern airliners use strap down systems because they have no moving gimbals to wear out.
Example Sentence 2
Because the strapdown system has no moving platform, it can begin alignment as soon as power is applied on the ramp.