High Flying Concern

Technologically advanced IFF are being used to protect aircraft from being accidentally shot down

Air Cmde Trilok Chand (retd)

Main concern of the Fighter/Bomber aircraft pilot re-entering own territory after a mission has been the friendly fire it might encounter while flying over the Tactical Battle Area (TBA). Historically, many aircraft have been lost in this manner during various campaigns. Usually, ground-based forces fear adversaries’ air forces more than they respect their own. These days, ground forces have been equipped with all kind of weapons to protect themselves against potential air attacks.

An Indian Air Force SU-30MKI touches down at Mountain Home Air Force base, United States

Presence of missiles of various kind and Air Defence (AD) guns in the TBA not effectively integrated into the broader national AD network have the potential to mistakenly fire at own aircraft. The National AD network is usually responsible for the air defence of the entire airspace, Vulnerable Areas (VAs) and Vulnerable Points (VPs) spread across the country. It is responsible for identification of all the flying objects in the airspace to segregate friend form the foe. The number of flying objects is likely to increase manifold with the Unmanned Aerial Systems (UAS) taking to sky. UAS or RPAs (Remotely Piloted Aircraft) as they are more familiarly called by the Directorate General of Civil Aviation (DGCA) would usher in many uncertainties in the command and control of the flying objects.

All flying aircraft, military or civil are required to be identified while flying over own airspace. Usually, civil aircraft fly on predetermined routes according to a predetermined schedule. It is easy to identify them procedurally or through technological solutions. That is not the case with military aircraft which are required to fly as per mission requirements dictated by operational considerations. An incoming aircraft from across the border could be a friendly aircraft returning after a mission or it could be an adversary’s strike mission heading towards important targets. Under such circumstances, technological solutions are more reliable. Procedural solutions are also used to complement the technology.

Technological solutions have evolved over a period of time. Primary surveillance radars with both transmitter and receiver at ground station and with no corresponding equipment on board the aircraft were able to pick up flying objects at long distances, but they could not be used to discriminate between friend and foe. Secondary surveillance radar systems with transmitter and receiver on board of the aircraft as well became handy for identification. The ground tans-receiver or interrogator would send interrogation signals and flying aircraft trans-receiver or transponder would send reply signals which along with the primary radar echo would result in the identification of the aircraft.

As the complexity of the aircraft and aerospace traffic increased, so did the identification requirements which were met by increasing the number of modes of operation of the secondary radar trans-receiver equipment.

Presently, this development has reached a level where Identification Friend or Foe (IFF) Mk XII and IFF Mk XIIA systems are in operation. This simply speaking could be described as a 12th major iteration in the development of the secondary radar system used for the IFF purpose. Number of modes of operation of this system has also reached five. There are modes which are specifically meant for the military aircraft as they have to undertake unpredictable missions at unpredictable times. Availability of a serviceable IFF system both on board of the aircraft and at ground radar station is a mandatory requirement. A newer Automatic Dependent Surveillance-Broadcast (ADS-B) system is also available and is in use by few countries.

In this surveillance technology, an aircraft determines its position via satellite navigation and periodically broadcasts it, enabling it to be tracked. The information can be received by air traffic control ground stations as a replacement for secondary surveillance radar, as no interrogation signal is needed from the ground. It can also be received by other aircraft to provide situational awareness and allow self-separation. ADS-B is automatic as it requires no pilot or external input. It is dependent as it depends on data from the aircraft’s navigation system. The Airports Authority of India (AAI) has commissioned ADS-B ground stations at all important airports in India.

Out of the five modes of operations of the IFF systems for military aircraft these days, modes one, two, four and five are used by the military aircraft only and there too, modes four and five are designated for use mainly by the NATO forces. Mode one is used for identification of the aircraft type or mission and code is selected by the pilot from the cockpit. Mode two is used for identification of the aircraft per se and code for this is entered by the ground crew in fighter aircraft. Mode four uses a three pulse encrypted reply and Mode five employs a cryptographically secured version of Mode S and ADS-B GPS position. Mode five IFF is the newly developed encrypted data link between interrogators and transponders and is used on MK XIIA IFF system using mode four and mode five. Modes A, B, C, D and S are employed for civilian use. Mode 3/A is used by military as well as civilian aircraft. This mode is often combined with Mode C to provide altitude information as well. Mode A and C responses are used to help air traffic controllers identify a particular aircraft’s position and altitude on a radar screen, in order to maintain separation. Mode S transponders are compatible with mode A and C Secondary Surveillance Radar (SSR) systems. This type of equipment is used for Airborne Collision Avoidance System (ACAS) also. New DGCA policy requires that all RPA (except Nano and Micro category operating in uncontrolled airspace) intending to operate in controlled airspace up to 400 feet (120 m) above ground level shall be equipped with the SSR transponder (Mode ‘C’ or ‘S’) or ADS-B equipment

Several reputed companies worldwide design and manufacture IFF systems. Raytheon and Thales have earned a good name for themselves and major share of business also. In India, Bharat Electronics Ltd (BEL) has been associated with the IFF systems for a long time now. Among other aircraft, its IFF system has been installed on the US, P-8I Long Range Maritime Reconnaissance aircraft for the Indian Navy. IFF Mk XII of the BEL uses state of art technology and has many user-friendly features. Hindustan Aeronautics Limited (HAL) Hyderabad also manufactures IFF systems. Manufacturing of CABS designed IFF Mk XII system has been taken over by the private companies as well.

In addition to airborne platforms, the IFF systems are also used on several naval platforms and ground-based surface to air missile systems as well. Prolonged negotiations leading to the signing of Communication Compatibility and Security Agreement (COMCASA) between the US and India on 6 September 2018 during the 2+2 dialogue were centred on India specific requirements as Indian defence forces use such equipment originating from different countries not party to encrypted data links and advanced NATO specific IFF modalities. India may soon have to opt for adoption of all available spoof-proof technologies for the IFF systems spread across all platforms irrespective of their origin.


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