GNSS Technology Force Enablers for Airborne Operations on the C-130-J-30 Super Hercules

This article discusses the use of GNSS technology as a force multiplier during Airborne Operations (ABNOPS) using the C-130-J-30 Super Hercules at an UNCLASS level.

This article will discuss the use of Global Navigation Satellite Systems (GNSS) as a force multiplier during Airborne Operations (ABNOPS) using the C-130-J-30 Super Hercules at an UNCLASS level. The report will establish the role of GNSS as both a force enabler and a force multiplier for the joint ADF Warfighting function of Force Generation, linking doctrine to current military inventory and mission roles on the C-130-J Super Hercules.

The use of GNSS systems to enable ABNOPS will be discussed with respect to both Airdrop and Airland mission sets, most notably using Joint Precision Airdrop System (JPADS), Instrument Meteorological Conditions Airdrop (IMC-Airdrop), the Terrain Awareness and Warning System (TAWS) and potential future use of the Joint Precision Approach Landing system (JPALS). The discussion will focus on the use of the Global Positioning System (GPS) by Lockheed Martin, including its capability, limitations and vulnerabilities.

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Airborne operations (ABNOPS): An air activity conducted to deliver personnel, material or special forces into a contested objective area that is enemy controlled or politically sensitive. This may be achieved by airdrop or airland from aircraft [RAAF Air Power manual, 2020]

Airborne operations as defined by the Air Power Manual is the act of insertion of personnel, materiel or Special Forces into a contested objective. This could be as simple as a day Airdrop mission to resupply a Forward Operating Base (FOB),  Humanitarian Aid and Disaster Relief (HADR) to remote Pacific islands, or as complex as a low-level approach and landing at night in a Radar Threat environment to an unlit and unsealed austere airstrip; termed ULUS (Un-Lit Un-Sealed).

Currently, the Royal Australian Air Force uses a fleet of 12 Lockheed Martin C-130-J-30 Super Hercules aircraft to fill the role of tactical airlift.

These aircraft are capable of inserting litters of up to 80 static line paratroopers or Military Free Fall jumpers, 18x2000lb containers or larger platform airdrop loads such as bulldozers or rigid hull inflatable vessels of up to 42,000 lbs. Long Range external tanks and upgraded engines allow the Super Hercules to carry up to 60,000lb of fuel and cruise in excess of 320 knots at 30,000ft or 210 knots (low level) for over 12 hours.

Dual Enhanced GPS INS (EGIs) and sophisticated instrumentation including Heads up Displays (HUDs), Heads Down Displays (HDDs) and a Flight Management System allow the two pilots to fly in ‘all weather, day and night conditions’; providing an unrivaled ABNOPS capability.

RAAF C-130-J30 Super Hercules conducts a mass Container Delivery System
Figure 1. RAAF C-130-J30 Super Hercules conducts a mass Container Delivery System (CDS) airdrop trial; 22x2000lb drop from the double CDS system [Air Power Manual, 2020] 

The navigation suite on the C-130J-30 Super Hercules is highly sophisticated; despite being designed and produced over two decades ago it is still in production by Lockheed and supported by software block upgrades. The EGIs use an Aircraft Based Augmentation system (ABAS) to improve the navigation performance of the GPS, comparing their position solution against accurate INS units as well as dead reckoning from conventional ground based navigational aids such as VOR, TACAN and NDB systems.

As a result, the EGIs provide extremely accurate and integrity monitored position information to the pilots through the Heads Up Display, Head Down Display and the Flight Management System. This enables crews to position themselves on extremely accurate tracks while low flying visually at night using Night Vision Devices (NVDs) in low light conditions.

There is an increasing emphasis on night operations within military aviation [Revell et al, 2004] and accurate navigation is the core foundation for ULUS operations; which allow crews to land on austere unlit and unsealed airfields in the vicinity of 30 feet wide in near complete darkness.

It is important to realize that even when crews are aided by NVDs, there is still a requirement for a minimum threshold of background illumination to achieve the appropriate level of definition to fly visually and avoid obstacles. With current generation equipment this is around 2 millilux, or that provided by starlight on a clear night.

C-130-J-30 Super Hercules operating on an austere airfield
Figure 2: C-130-J-30 Super Hercules operating on an austere airfield

Despite extremely sophisticated equipment, Current ABNOPS Techniques, Tactics and Procedures (TTPs) rely heavily on visually sighting and clearing objectives. For example visually sighting a Ram Air Marker (Flare, Smoke or Infrared Strobe) prior to an airdrop, or low flight at night (below instrument safe altitudes) using flying with visual reference to the ground at night using Night Vision Devices (NVDs), called Visual Maneuvering Height missions (VMH).

This places an inherent limitation on the crew’s ability to achieve mission outcomes due to vagrancies of the prevailing meteorological conditions of Cloud base, Visibility, background illumination levels, commensurate with the crews experience and fatigue levels.

Furthermore, traditional airdrop operations commonly use unguided parachutes which are subject to crosswind, rigging and release timing errors; albeit these errors are minimized by using minimum drop heights. Crews are typically able to achieve strike reports within 100ft of the intended Point of Impact (PI) visually. Drop Zones (DZs) are traditionally the size of small airfields or sporting ovals to accommodate for these errors, placing limitations on practical airdrop use.

Modern GNSS technology can be used as ABNOPS force enablers and multipliers; firstly in terms of enabling ABNOPS in non-visual conditions, and secondly by allowing precision airdrops, for example to resupply troops in contact.

Joint Precision Air Drop System (JPADS)

JPADS integrates modern GNSS technology into extant ABNOPS procedures by embedding GPS receivers and steerable high performance (drive) parachutes onto air droppable loads. This allows crews to accurately drop loads ranging from 500 to 4000lbs without ever sighting the target PI, in most weather conditions (JPADS are not suitable for flight through icing conditions or heavy rain which can result in system loss).

Using a high performance steerable chute with its own GPS satellite navigation system means that once programmed and released, the JPADS container can effectively ‘self deliver’ with ranges in excess of 30km depending on release altitude, payload weight and prevailing winds.

Joint precision airdrop system JPADS
Figure 3: Airborne JPADS container. Note the steerable chute, antennae and trailing arm [RAAF, 2019]

Depending on wind conditions and GPS signal, JPADS can land with an uncertainty of approximately 300ft on ‘point DZs’, or laterally within a stretch of road in ‘linear DZ’ mode. This provides a stand-off precision Time on Target (ToT) airdrop capability for threat environments which would normally preclude ABNOPS (such as radar threat environment based on current generation air defense weapons).

Airdrop trials using the Hercules have seen strike reports well under 100ft and within 6 seconds ToT, but there is no UNCLASS information regarding their accuracy in a GPS denied environment at this stage. 

Instrument Meteorological Conditions Airdrop (IMC-Airdrop)

IMC Airdrop techniques allow pilots to apply conventional ABNOPS airdrop procedures to instrument flight; that is, airdrop conventional loads without visual acquisition and clearing of a drop zone. In a similar manner to how an instrument approach is flown to an airfield in poor weather conditions, an IMC Airdrop card is created preflight to map obstacles and minimum flight altitudes along corridors leading to an airdrop release point.

This is only made possible due to the accurate position information provided by the aircrafts EGIs (of which GPS is used to overcome drift in the INS), as well as accurately charted topographical maps produced via satellite tracking and mapping for preflight mission planning.

Instrument meterological conditions airdrop IMC airdrop
Figure 4: C-130J-30 Super Hercules conducting IMC airdrop at night. Left – pilot flying with reference to instruments and using NVDs, and right – dual CDS load exiting the aircraft from load station 750.

International aviation practice requires pilots to provide at least a 1000ft vertical clearance of charted obstacles, and 1360ft vertical clearance of potential uncharted obstacles. Special dispensations are afforded to the military under their Military Type Operator Certificate and Statement of Intent; this allows pilots to act in accordance with their Standing Instructions to reduce this vertical safety buffer to achieve lower airdrop release altitudes and hence more accurate drops onto smaller DZs.

This may allow pilots to get a visual below a cloud base and drop visually or instead to simply conduct the airdrop in cloud or below required visibility or illumination levels. This provides mission assuredness.

Enhanced Ground Proximity Warning Sensors (EGPWS)

The C-130-J-30 features an Enhanced Ground Proximity Warning Sensor (EGPWS) system which prevents Controlled Flight Into Terrain (CFIT) accidents. The Terrain Awareness and Warning System (TAWS) is a major constituent of the EGPWS which compares the aircrafts navigation solution (from the EGIs) to an obstacle database loaded to the aircraft, and graphically displays this via an augmented (tinted) topographical map. TAWS obstacle databases are only made possible due to satellite terrain mapping. 

Enhanced ground proximity warning sensors for Terrain Awareness and Warning System HDD display
Figure 5: C-130-J-30 TAWS display on HDD#1. Note Magenta in this case represents terrain above the aircraft, and so provides pilots with situational Awareness on terrain contouring for efficient terrain masking against threats.

In flight during VMH or ULUS missions, the aircraft Captain will configure Head Down Display (HDD) #1 to TAWS which enables a quick scan for situational awareness. If pilots ignore this map and an obstacle penetrates the aircrafts protection envelope, special alerts will annunciate to warn the crew. 

The other constituent of the EGPWS is the Ground Collision Avoidance System (CGAS) which uses Radar Altimeter measurements, Attitude and Rate of Descent as well as instrumentation such as the glidepath signal on an Instrument Landing System to ensure defined safe flight envelopes are not exceeded leading to CFIT.

Joint Precision Approach Landing System (JPALS)

JPALS is a system used to guide aircraft to a runway in poor weather conditions, similar to a conventional Instrument Landing system. Rather than relying on a Localizer beam for azimuth guidance and a glide path beam for vertical (height) guidance as a conventional Instrument Landing System would, JPALS is a differential GPS based system using a ground GPS receiver and transmitter and is a Ground Based Augmentation System (GBAS) to guide aircraft.

Modern Differential GBAS stations can enhance GPS location uncertainty from an average of approximately 15m down to as accurate as 10cm. Initially created out of necessity when Selective Availability artificially limited GPS accuracy, D-GBAS correct for GPS errors caused by clock drift, ionospheric effects and inaccuracies in ephemeris data.

A GBAS would be required for this level of precision approach capability, as Space Based Augmentation Systems (SBAS) such as the Wide Area Augmentation System (WAAS) does not provide a precision approach capability [Kavanagh, 2015].

JPALS is mostly used on aircraft carriers and amphibious assault ships to aid aircraft recovery in poor weather, and has been in service for some time including operationally with the Joint Strike Fighter aboard USS Wasp [Raytheon, 2020].

The MQ-25A Stingray multi-mission unmanned aerial vehicle under development is currently planned to be equipped with JPALS; the future looks increasingly autonomous and GPS enabled.

ULUS approaches are a form of ABNOPS and subset of VMH which are hand flown using NVDs to visually avoid obstacles during a tactical approach to visually acquire the landing threshold.

Comprehensive Objective Area Analysis (OAA) and study of the landing environment is required as well as a high level of skill to quickly visually acquire and correct aim point deviations to safely touchdown with mission assuredness.

C130J hercules ULUS approach unlit unsealed night vision device, GNSS technology
Figure 6: C-130-J-30 Super Hercules as viewed through a Night Vision Device on a ULUS approach

Expeditionary ABNOPS such as ULUS approaches could be assisted by discreet JPALS ground stations. These could conceivably be forward placed by JPADS airdrops and assembled by Special Forces if required in less than 60 minutes, however most current JPALS systems are vehicle plus trailer mounted.

Raytheon claim that their Expeditionary JPALS system can provide precision approach capability in challenging deployed terrain conditions down to accuracy of within 1 ft, and could be pre-programmed with up to 50 different approaches to aim points within a 20 nautical mile radius [Raytheon, 2020].

The implication is that the JPALS could couple with the autopilot in a similar manner to a conventional ILS with a Decision Altitude (DA) from which a pilot would need visual reference to the landing environment (currently the C-130-J-30 is not approved for auto land operations). This provides additional ABNOPS airland mission assuredness during periods of poor weather.

The ability to conduct a penetration descent from safe altitudes down through a Weapons Engagement Zone without the problem of having to level off at a lowest safe altitude try to ‘get visual’ reduces mission risk and risk of crews being engaged. Even if JPALS did not terminally guide aircraft to a landing DA, it could provide a deployable ‘dummy approach’ from which aircraft could safely get visual in a challenging terrain scenario and then proceed onward via VMH to a ULUS approach.

Matt Gilligan, the Vice President of Raytheon Intelligence and Space has publically stated:

“JPALS can help any fixed or rotary-wing aircraft land in harsh, low-visibility environments.”

[Raytheon, 2020]

Operational effectiveness

The RAAF is critically dependent on its networks, data links and information for its ability to project force [Air Power Manual, 2013]. The reliance on a GNSS system for precision navigation during ABNOPS missions is one aspect of this – termed a centre of gravity or critical vulnerability.

GNSS Jamming and Spoofing is a threat in the modern battle space; jamming is a  technique commonly employed by both state and non-state actors due to their relative ease and low cost of entry, whereas spoofing typically requires a sophisticated state based actor due to its complexity.

Degrading GNSS satellite signals falls under the classification of Electronic Warfare, as a form of military action to exploit the electromagnetic spectrum – This can be classified as either Electronic Support, Electronic Protection or Electronic Attack.

Electronic Attack is defined by the Air Power Manual as:

Directed energy to attack personnel, facilities or equipment with the intent of degrading, neutralizing or destroying adversary combat capability

[Air Power Manual, 2013].

This has significant legal implications under extant Rules Of Engagement (ROE), potentially allowing those conducting jamming or spoofing activities to be designated as targets for kinetic attack.

Relying solely on GPS for aircraft navigation during critical phases of flight or for targeting would never pass airworthiness or battle worthiness boards, even when military GNSS receivers are deemed to be ‘hardened’ using military encrypted P(Y) codes.

Aircraft Based Augmentation Systems designed by Lockheed go some way to mitigating this threat, as is currently used in within the aircrafts EGIs which integrate GPS systems with inertial navigation [Grewal, 2013]. Additional augmentation such as Ground or Space based augmentation provides a promising area of interest for increasing the accuracy, integrity and reliability of military GNSS satellites and equipment.

There is a subtle shift away from the conventional GPS system as we know it (Space, User and Control segments), and towards a new system called ‘Precision Navigation and Timing’. PNT systems could be considered as a four segment system, with a growing reliance on GPS Augmentation for increased resilience (Space, User, Control and Augmentation segments).


Jamming is the interference of a signal to prevent or degrade its ability to be received. Jamming GPS signals can be achieved relatively simply, using either broad spectrum or narrow band jamming.

Broad spectrum jamming at its simplest is just broadcasting a spectrum of ‘noise’ and hoping it masks any frequencies in use, whereas narrow band jamming of GPS is a more targeted attack of the L1 and L2 band carrier signal frequencies (1575.42 and 1227.6 MHz respectively) designed to deliberately interrupt GPS communication [IS-GPS-200K, 2019].

 Jamming is easy to achieve because of the weak signals received from satellites owing to their high orbits IVO 20km.

“Even a 10W jamming device can deny GPS coverage for a large area”

[Securing military GPS from spoofing and jamming vulnerabilities- Cole, 2015].

A Notice to Airmen (NOTAM) issued during jamming tests by the US Naval Air Warfare Centre Weapons Division in China Lake, California warned that their 500W jammer could result in unreliable GPS signals up to 300 nautical miles from the test range [Brewin, 2001].

The jamming signal can prevent GPS receivers from acquiring satellites by masking the C/A signal, and can interrupt established L1 and L2 links, regardless of encryption.

Jamming is most frequently conducted by a ‘low tech’ adversary using ground based transmitters, which may even be elevated for maximum operational effectiveness. Typically this doesn’t impact aircraft operations at altitude as heavily as ground based users such as vehicles since aircraft GPS antennae are usually positioned on top of the aircraft.

It does affect aircraft on the ground or in terminal phases of flight; for example positioning a ground based jammer on a ridgeline IVO Kabul airport could deny GNSS-RNAV approaches to the airfield and also lower aircraft navigation solution Figure of Merits. This could have the effect of causing an aircraft to divert to an alternate airfield, or force an aircraft onto the Kabul airport Instrument Landing System (conventional ground based navigation transmitters).

Flight paths on the ILS are well known and openly documented and as such the aircraft could then be directly targeted by ground fire. 

In a conventional threat environment, aircraft like the American Boeing EA-18G Growler or Chinese Shenyang J-16 can be used to conduct aerial jamming of GPS signals (amongst other things like radar and communications jamming).

The ALQ-99 and ALQ-218 ‘High and Low band’ pods fitted to the EA-18G Growler are specifically designed to achieve this.

Russia is becoming a world leader in EW systems; especially ground and drone based jamming. Russian EW activity is frequent in Syria and Ukraine where it has been highly effective in denying and degrading the use of GPS amongst other signals, and has caused issues with commercial aircraft navigation as far as Israel [Egozi, 2019].

General Raymond Thomas, the former commander of United States Special Operations Command (SOCOM), described Syria as the most aggressive EW environment on the planet” [Clark, 2018].  US SOCOM have previously destroyed significant numbers of Russian supplied jamming equipment in Iraq [Al Rodhan, 2012].

Russian Borisoglebsk (left), Krasukha (middle) and Moskva (right) Jammers.
Figure 7: Russian Borisoglebsk (left), Krasukha (middle) and Moskva (right) Jammers. These systems have been identified in Syria, and used extensively during recent conflict with Ukraine to mask GPS signals to deny the use of drones and GPS navigation.

Modern block III-A PNT satellites are fitted with higher transmitter power antennas, and backed up by spot beam antennas which allow the satellite to concentrate a ‘better’ signal within a discreet area of interest [Lazar, 2002].

Because the Energy per Bit to Spectral Noise density ratio (Eb/N0) of the link is increased, the result it is more ‘jam resistant’ PNT solution. Spot beams can be used as a real-time counter-jamming technique for contested areas, or preemptively used to provide better coverage vulnerable areas such as airfields or FOBs.

Currently there are three Block IIIA PNT satellites in orbit (The latest of which was launched aboard a Falcon 9 in June 2020) with a further 7 planned launches. Higher Eb/N0 signals from these new satellites creates the need for stronger and more sophisticated jamming equipment in an evolutionary ‘EW arms race’.

The EGIs on the Super Hercules are deemed ‘Jam resistant’ and capable of functioning in GPS degraded or GPS unavailable modes. The aircraft features dual Mission Computers (MC), which constantly cross check the integrity of the navigation solutions being input into each EGI; GPS 1, GPS 2, INS 1 and INS 2.

The Crew are alerted to a GPS degrade or GPS Fail condition via Advisory, Caution and Warning System (ACAWS) alerts, and the active MC will automatically isolate suspect channels and bias its navigation solution toward the Inertial Navigation System.

In a completely GNSS denied environment due to targeted jamming, the EGIs can only provide a degraded navigation solution which would preclude the use of GNSS-RNAV instrument approaches once the navigation FOM drifts to unacceptable levels. Furthermore, because JPADS uses its own self contained GPS suite, JPADS could not be used effectively in a GNSS denied environment.


Spoofing is a way of deceiving Global Navigation Satellite System receivers and is a theoretical risk for military and government operations. Although there is limited unclassified information available about GNSS spoofing, theoretically spoofing could be used to ‘trick’ a receiver into thinking it is somewhere when in fact it is not. The University of Texas at Austin Cockrell School of Engineering conducted an experiment that successfully spoofed a civil GPS on an $80M ‘Superyacht’ sailing off the coast of Italy.

Using a device created by researchers and operated by a student at the University of Texas, they successfully coerced the vessel off course without triggering any alarms. The spoofing signals mimicked the civil GPS L1 signal, and were slowly increased until they ‘drowned out’ the legitimate signal and effectively took control of the receiver.

The attacker then tricked the receiver into thinking it was drifting off course (when it was actually on course) by providing false timing information, and the ship was made to deviate [Humphreys, 2013].

Due to the security of the encrypted P(Y) or ‘M-code’ signal on the L2 frequency, it is considered unlikely that military or government users will be subject to spoofing.

To conduct spoofing of P(Y) or ‘M-code’ encrypted L2 signals would require very complex signal-generation equipment to track the vehicle and exactly match its trajectory before spoofing; there are simpler [and cheaper] ways of engaging – like shooting it down” [Cole, 2015].

Furthermore, Block IIF and III-A GPS satellites launched by the US DoD feature the latest in encrypted GPS software (updated ‘M-codes’) for increased cyber resilience [Cole, 2015], [Barker et al, 2006]. Whilst the encryption does not prevent signals being jammed, the secure link works to prevents spoofing.

GPS Block IIF and above signals architecture
Figure 8. GPS Block IIF and above signals architecture [Barker et al, 2006]

The implication is that whilst Australia is strategically partnered with the US and has access to their latest PNT (GPS) technology, Spoofing is unlikely to be a significant threat for the conduct of ABNOPS missions. Notwithstanding, intelligence reports still highlight spoofing as a potential threat from sophisticated adversaries who may wish to anonymously alter the outcome of conflicts.

As such, Emissions Control (EMCON) ABNOPS sorties are required to be trained for, planned and frequently rehearsed. These simulate operations in a GPS and wider signals denied Electronic Warfare environment, to keep crews trained and proficient.


GPS is used extensively on board the C-130-J-30 Super Hercules tactical airlift aircraft as a replacement for a navigator. From precise navigation, obstacle avoidance, airdrop and even potentially future airland operations using JPALS, the GPS embedded in the aircrafts EGIs act as a critical force enabler and multiplier. This allows the Hercules to perform the joint ADF Warfighting function of Force Generation through ABNOPS.

Operating in a modern battle space means the Hercules is vulnerable to Electronic Warfare; Electronic Attack against its GPS systems could occur in the form of jamming or spoofing. Whilst the military PNT system integrated into the Hercules uses L2 signals encrypted with P(Y) and ‘M-code’s to prevent spoofing, it is still vulnerable to jamming of the C/A, L1 and L2 signals.

This is especially so when conducting ABNOPS such as low flying in contested environments against modern advisories. Even relatively inexpensive GPS jammers can produce sufficient targeted noise to degrade the aircraft navigation solution FOM, which can result in operational effects.


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ken johnson


Ken is a passionate aviator, a professional pilot and flight instructor. He has over 17 years of flight experience across hundreds of aircraft ranging from recreational, aerobatic, historic, commercial and military aircraft, training hundreds of students along the way. Find out more.

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