The ILS is an invaluable aid to pilots, especially those operating to/from the many airports where poor weather is common (low-visibility operations would be completely impossible without an ILS); however, ILSs are expensive and maintenance-intensive, with the result that many smaller airports lack ILS capability. Also, the requirement for a considerable quantity of pre-emplaced infrastructure obviously precludes one from performing an off-airport instrument landing.

On the other hand, the technology is available to guide an aircraft down to a precision landing at an arbitrary point on the ground, and much of this technology is already mandatory equipment on aircraft; GPS (which most if not all aircraft already have anyway) could be used for horizontal positioning and guidance and for plotting a landing route about the local terrain, the radar altimeter (also standard aircraft equipment) would provide vertical guidance, and a forward-looking radar system (also already standard, in the form of the aircraft's weather radar, which should only require an additional driver or two to add a terrain-sensing mode) would allow fine control of the aircraft's flightpath for the landing itself (where GPS, with its ~10m CEP, is insufficiently precise and accurate for a safe touchdown) and allow the aircraft to orient itself in space (as GPS tells the aircraft where it is, but not which direction it's pointing). Additional equipment that would be useful and could easily be added would be a second weather radar (to allow the pilots to continue to monitor the weather even with one radar in terrain-mapping mode), a Doppler radar system (to warn the pilots of dangerous windshear, microbursts, etc.), and a forward-looking lidar system (to provide advance warning of clear-air turbulence along the approach path).

With the appropriate software, these instruments could be used to plot and fly a safe instrument landing at a noninstrumented airport, or even at a non-airport; this latter capability would be extremely useful for medevac and SAR pilots (whose duties, by their very nature, involve operations to and from off-airport locations, frequently in poor weather) and for military helicopter pilots (same reason).

Are there any aircraft already equipped with such a "self-contained ILS"?

  • 6
    $\begingroup$ Why on Earth would you think that most aircraft have radar altimeters and forward-looking radar? Or radar of any sort? And how much is this going to cost me, and is the weight more than my Cherokee's payload? $\endgroup$
    – jamesqf
    Commented Dec 4, 2018 at 5:18
  • 1
    $\begingroup$ This question editorializes about varied needs and technologies, but asks the question about "self-contained ILS." Perhaps the extended discussion distracts from the key question, about a self-contained guidance system, which has very specific functionality. In fact the ILS functionality is much more limited than the broad discussion that precedes it. $\endgroup$
    – mongo
    Commented Dec 4, 2018 at 14:59
  • $\begingroup$ GPS is not mandatory equipment $\endgroup$
    – Steve Kuo
    Commented Dec 4, 2018 at 16:44
  • $\begingroup$ Radar alts and radar are not standard equipment. Where did you hear that it was??? $\endgroup$
    – acpilot
    Commented Dec 4, 2018 at 19:03
  • 1
    $\begingroup$ Recommended reading: 2019 Federal Radionavigation Plan. It covers the systems currently available and future planned systems. $\endgroup$
    – Gerry
    Commented Mar 9, 2020 at 21:41

4 Answers 4


Approaches guided by GPS are called RNAV; it can provide both lateral and vertical guidance, in some cases to the same precision as ILS Cat I, without need for a radar altimeter--which is not standard equipment. (There are also non-GPS ways of using RNAV, which are mainly used by older airliners that haven't been upgraded yet.)

Note that standard GPS has accuracy of 100m; SBAS (aka WAAS) gets that down to 7.6m. Both are standard in aviation GPS units these days, and GBAS (aka LAAS) will eventually get that down even further.

There are already three times as many RNAV approaches as there are ILS approaches with more appearing every day, and most aircraft are now equipped to use them or probably will be soon. IOW, the essence of what you propose is already here.

Instrument approaches do have to be pre-planned to ensure obstacle and terrain clearance, so airplanes can generally only use them to land at airports. (The rules are different for rotorcraft, and that's generally what you'd use for rescue, but I'll have to leave the specifics to someone else.)

Many large aircraft carry weather radar, but it's too heavy for light aircraft; both can use satellite weather data services, in addition to getting weather updates via radio the traditional way.

  • $\begingroup$ Can't obstacle and terrain clearance be guaranteed by using GPS, the radar altimeter, and a forward-looking radar? An aircraft's GPWS (required by law in all countries) uses all of these to keep you from flying into the ground when you don't want to; presumably, they would be just as useful for guiding you to a landing on the ground when you do want to. $\endgroup$
    – Vikki
    Commented Dec 4, 2018 at 5:06
  • 1
    $\begingroup$ @Sean: GPWS (Ground Proximity Warning System) is not required on all aircraft, only (per Wikipedia) turbine-powered aircraft with more than 6 passenger seats. $\endgroup$
    – jamesqf
    Commented Dec 4, 2018 at 5:22
  • 1
    $\begingroup$ GPWS only looks straight down, so it can't detect sharp rises in terrain--and it is disabled when the aircraft is in a landing configuration anyway. EGPWS adds a terrain database and GPS lookahead, but it still only covers terrain; adding every man-made structure on Earth (and keeping it all up to date and distributed to every aircraft in a timely fashion) would be completely unmanageable. $\endgroup$
    – StephenS
    Commented Dec 4, 2018 at 6:06
  • $\begingroup$ For an example of an inhibited GPWS contributing to an accident see en.wikipedia.org/wiki/2010_Polish_Air_Force_Tu-154_crash $\endgroup$ Commented Dec 4, 2018 at 12:14
  • $\begingroup$ RNAV is not limited to GPS approaches. $\endgroup$
    – mongo
    Commented Dec 4, 2018 at 14:55

You don't need nearly all the equipment you mention. A great deal of aircraft are capable of flying GPS/RNAV approaches from big boys down to the little Piper Archer I fly. Units as small as a Garmin 430 are capable to providing all the facilities you need to fly GPS/RNAV approaches. If your unit has WAAS capabilities you can fly to even lower minimums.


This does exist, and is used by US military aircraft. It's called a Self-contained Approach (SCA) or Independent Precision Radar Approach (IPRA). The primary user of these approaches is Air Force Special Operations Command on aircraft like the MC-130 and AC-130.

Regulatory guidance is contained in the AFI 11-202v3 AFSOC Sup, section 7.4, and operational procedures would be governed by the applicable AFI 11-2MDS volume 3 or another MDS-specific publication, which may be a controlled item.

Shooting one of these approaches involves the flight crew looking for obstacles or obstructions; choosing the planned glideslope, and creating the plan, including update, missed approach, and descent points.

  • 1
    $\begingroup$ Thanks for the answer. This sounds great for emergency or tactical use. Is there an equivalent for civilian use? Would this still be considered a precision approach? $\endgroup$
    – Dean F.
    Commented Mar 9, 2020 at 17:06
  • $\begingroup$ I've never heard of anything similar in the civilian world, and doubt there is anything (not all military aircraft have the capability, and since even fewer civilian aircraft, if any, have the radar needed to perform this, I doubt there is anything there. I guess you'd call it a precision approach, since it has glidepath guidance, but really it's in its own category of approaches $\endgroup$
    – SSumner
    Commented Mar 9, 2020 at 17:19

An ILS approach consists of a minimum of a localizer and glide slope transmitters. Both transmitters are ground based, in a fixed location. While the creation of some other reference point, using GNS or even inertial navigation might be possible, it does not directly emulate ILS.

Furthermore, if one were to recreate the references to a landing zone using some other form of navigation, it is likely that the exact emulation of a localizer and glide slope might not be exactly emulated. Consider that MLS was intended to be an ILS substitute, and it offered a variety of localizer courses, and a variety of glide slope paths.

While it is true that self contained navigation systems, including INS, and even varied techniques such as radar mapping, or even IR lidar mapping, could be employed, it is unlikely and perhaps inefficient to have them emulate what an INS does. Therefore the likelihood of a "self contained ILS" appears to be very close to zero.

While there are many systems and methods which will navigate to a given point, with the potential ability to align an aircraft for a landing, they do not match the essentials of an ILS, which is two ground based transmitters, one with lateral and the other with slope (vertical) guidance.

Finally, if one wants to consider self-contained navigation approaches, a study of missile guidance will yield scores of self-contained, and externally augmented approaches.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .