Do today's aircraft still have INS (inertial navigation system)?

Question

Do today's new aircraft like Boeing 787 still have INS (inertial navigation system)?

Answer 1

Short answer

Aircraft still use inertial navigation systems because INS is autonomous, it doesn't need any external support to work, it provides more information, and is more accurate than a GNSS in the short term. There is no plan to stop using it.

On the contrary, INS is required for certain operations. For instance the B787 cannot be flown without at least one IRU operative. See B787 Master Minimum Equipment List MMEL, item 21-01-01 page 182.

The usual solution for air navigation is to use INS, frequently updated by GNSS to contain drift, as long as GNSS signal is available, accurate and reliable (professional GNSS receivers are able to determine their reliability).

^{GPS/INS sensors fusion, source}

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Details

While INS has several disadvantages, namely initial alignment time and drift, it has also unique capabilities:

• INS is autonomous, position is determined without external cooperative support.

• INS position can be updated 1,000 times per second.

• INS provides position information like GNSS, but also orientation (attitude), rotation rate and related accelerations. In the short term these data are very accurate. For example, the yaw damper uses instantaneous motion data to counter Dutch roll.

• INS provides True North direction.

On the other hand, global navigation satellite systems (GNSS):

• Contrary to inertial navigation systems (INS), are dependent on a lot of factors to work, including space vehicles, ground stations, antennas, or solar activity.

• GNSS signals can be obstructed, altered or jammed.

• GNSS is updated at a slow rate (e.g. once or 10 times per second, that is by increment larger than 20m for an airliner at Mach .85), due to the heavy computation required to extract and process the weak GNSS radio signal.

• The best known GNSS, the American Navstar GPS, is a military system funded and managed by US Air Force.

• While GPS is in effect always accurate for civil uses, it must be remembered there is no guarantee from the US DoD on that. The Navstar GPS operational specifications for SPS (civil) service allows for 72 minutes per day (2σ / 95th percentile) with a DOP > 3, that is more than 17m horizontally and 37m vertically. During these 72 minutes, the error is unlimited.

In the field of aviation, GNSS and INS are more and more coupled with air data and magnetometers, that's called data/sensor fusion to take the best of each system, cross check results and detect sensor failure.

As a everyday life example: Without an inertial sensor in a car "GPS receiver" (more accurately: a GPS-aided navigation system), the navigation system would be helpless at roundabouts. The GPS receiver instantaneous precision, its low update frequency, and its lack of orientation sensing would prevent it to correctly derives the actual position and the closest roundabout exit.

Answer 2

To answer the specific question on the 787, yes.

According to this article

Boeing 787 avionics overview

Rockwell Collins provides the flight deck display system, pilot controls....Earth reference system (inertial navigation)....

In the more general sense pretty much all the big stuff flying (as far as I know) still has an INS unit. This may be due to the aircrafts age in that it simply comes from a time this was cutting edge. In the newer case they are still used to cross check GPS accuracy you can find more on in this answer (and dangerously close dupe).

Answer 3

Absolutely. Both intercontinental civil aircraft and military aircraft are equipped with GNSS updated solid state INS systems using ring laser gyros for positional detection and navigation.

Answer 4

Modern aircraft have an “inertial reference system”, which has the set of gyroscopes and accelerometers and is used to feed all systems that need those data.

The attitude, its rate of change, and accelerations (vertical acceleration is wing loading, lateral acceleration approximates side-slip) are used for:

• Attitude indicator, obviously.
• Also heading indicator.
• Pitch and roll flight envelope protection on aircraft that have it (Aribus from A320 on, Boeing from 777 on and some other).
• Autopilot and yaw damper. Altitude and heading respond too slowly to changes in control input, so those modes also need attitude and accelerations as intermediate references.
• Flight laws. On Airbus even the manual control selects wing loading and roll rate and the actual control surface deflection is calculated by the computer, so it needs the wing loading (vertical acceleration) and attitude values.

The position is integrated. This means it accumulates error over time. However, there is never large error over short time. It can be also updated at high rate, usually 100 to 1000 times a second.

On the other hand, GNSS (e.g. GPS) does not accumulate error, as it does not rely on the previous measurement when doing the next, but it has slower update rate, usually only 1 per second, and it oscillates around the actual position with variable error magnitude of which can only be estimated to limited degree.

Therefore combining the two systems give some advantages:

• INS interpolates the position, providing higher rate of updates to the autopilot, so it can follow defined route more precisely.
• Since each system has different kind of error, cross-referencing them provides higher accuracy then either system alone.
• INS provides fall-back in case GNSS (which may fail or lose precision for external reasons) fails. This is especially important when flying Required Navigation Performance (RNP) procedures. These are in places with limited terrain clearance like narrow valleys. If GNSS fails, the INS allows enough time to safely climb out of the terrain (and divert) before it accumulates too much error.