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

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Short answer

Aircraft still use inertial navigation systems because INS is autonomous, it doesn't need any external support to work. 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.


Details

A global navigation satellite system (GNSS), contrary to an inertial navigation system (INS), is 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. The most known GNSS, the American Navstar GPS, is a military system funded and managed by US Air Force, not by civilians.

The usual solution for navigation is to use INS frequently updated by GNSS, as long as GNSS signal is available, accurate and reliable. GNSS receivers are fitted with a system able to determine when this is not the case.

While INS has several disadvantages, it has also unique capabilities:

  • INS position can be updated 1,000 times per second while GNSS is updated at a slow rate (e.g. once or 10 times per second), due to the difficulty to extract the weak GNSS radio signal and to the heavy computation involved.

  • INS provides position elements like GNSS, but also orientation (attitude), rotation rate and related accelerations. In the short term these data are very accurate.

  • INS provides True North direction.

In the field of aviation, sensors like GNSS and INS are coupled with air data and magnetometers, that's called data/sensor fusion.


Related

GPS navigation systems used in cars usually combine a GPS receiver and small mechatronics inertial/magnetic elements, so that the position continues to be updated in tunnels and underground parking lots, and so that turns are detected instantly.

Without the INS sensor, the navigation system would have a hard time in roundabouts. The GPS receiver instantaneous precision, its low update frequency, and its lack of orientation sensing would prevent it to correctly discriminate exits on a medium-size roundabout.

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    $\begingroup$ Do aircraft really use 1Hz GNSS? Receivers with 5Hz and 10Hz capability have been widely available for some time now. $\endgroup$ – hobbs Aug 29 '17 at 14:50
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    $\begingroup$ @hobbs: You're right. That's still a large "blind distance" between fixes. 1 Hz is 280 m at 1,000 km/h, 10 Hz is 28 m. $\endgroup$ – mins Aug 29 '17 at 19:22
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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).

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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.

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  • $\begingroup$ Can confirm that the T-38, F-16, and F-15 utilize RLG INS systems - sounds like they work pretty well, especially when linked to GPS positional updates $\endgroup$ – ANDY-S Aug 29 '17 at 4:15
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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.
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