By: Irish D. Torres, Safran Navigation and Timing

For much of modern aviation and defence, dead reckoning feels like a relic of the past, a method associated with early navigation, long before satellites provided instant positioning anywhere on Earth.
But as reliance on GPS deepens, and its vulnerabilities become harder to ignore, this once “outdated” concept is finding renewed relevance.
Given today’s contested environments, where satellite signals can be disrupted, denied, or manipulated, inertial navigation systems (INS) are stepping back into the spotlight, not as a replacement for GPS, but as a vital foundation for resilience when external signals can no longer be trusted.

Dead reckoning, put simply, is based on the calculation of the current location relative to some reference point concerning speed, heading, and time.
Modern-day inertial navigation systems push this notion even further by utilising highly advanced sensors, especially accelerometers and gyros, with their exceptional capacity to sense even the slightest changes in movement.
That capability allows INS to calculate one’s position independent of any external input.
As compared to satellite navigation systems that depend on signals from space, inertial navigation is completely immune to jamming and spoofing.

Notwithstanding its strengths, there are some disadvantages that should be considered when applying this technology.
Firstly, the main problem of this method lies in drift.
Despite the fact that modern devices can make precise measurements, sooner or later, they will inevitably all encounter some level of error. With time, errors will build up, resulting in less precise positioning.
In precise systems, this drawback may negatively impact the usability of the INS technology alone. In terms of GPS spoofing, the situation shifts.
Without access to satellites, having an alternative method for determining position becomes more advantageous than achieving pinpoint accuracy.

With the rise in occurrences of GNSS interference, it appears that inertial navigation is no longer considered a backup system, but rather an integral part of navigation strategy.
It enables platforms in aviation and the military industry to be aware of their situation when they have a signal outage. They can proceed with their course, keep their flight path steady, and fulfill their missions even when there is no GPS signal.
This is the essence of it.
Unlike GPS, inertial navigation was not made to substitute for GPS completely. Rather, it serves as an anchor, a buffer, and a source of reliability when everything else is unreliable.

Inertial navigation becomes truly valuable only when it is used alongside other systems.
Aerospace navigation today uses INS together with GPS, radio navigation facilities, and other data to provide the best possible resilience of the navigation process. When there are no issues, GPS gives precise global positioning, and INS stabilises the navigation process.
In cases when GPS is jammed or blocked, INS plays a greater role to keep the system working until the inputs become available again.
Given this change, companies like Safran are further developing their inertial navigation solutions by increasing the precision of sensors, reducing drift, and improving integration possibilities.
As a result, INS can operate for longer periods and with greater accuracy.

The emphasis on inertial navigation has caused changes in the approach towards training.
This entails an introduction of pilots and other operators to the art of dead reckoning, which has been brought back from its historical context into the realm of practical application. The importance of such understanding becomes clear when considering the possibilities of the unreliable functioning of the automation system.
From this perspective, the return to inertial navigation cannot be merely technological but also operational. It involves a wider realisation that resilience is not simply a matter of systems but also of those using them.

While GPS transformed navigation, inertial systems never truly went away. They continued to operate quietly in the background, supporting aircraft, stabilising systems, and providing redundancy.
What has changed is their importance.
In an era where satellite signals can no longer be taken for granted, inertial navigation is moving from a supporting role to a strategic necessity.

Navigation’s future is not going to be determined by one particular technology, but by the capability to integrate several systems at once. GPS will play an important role here, too, but it will not operate in isolation anymore.
And in that dynamic, inertial navigation will play a central role.
Because when external signals fail, and uncertainty begins to grow, the ability to navigate based on what you know, rather than what you receive, turns into something more than a fallback. It becomes the difference between losing your way and staying on course.