KJ-600: Eye in the sky for China’s future carriers

The Diplomat has published an assessment of what is known so far about China’s fixed-wing carrier-based airborne early warning and control (AEWC) aircraft. Caliber.Az reprints this article.

As of mid-2023, China’s People’s Liberation Army Navy (PLAN) has two ski jump (STOBAR) aircraft carriers in service and a single catapult (CATOBAR) aircraft carrier in fitting out awaiting sea trials. Additional CATOBAR carriers are expected to be produced in coming years, even if the exact timing and configuration of them are not yet known. 

One of the benefits that a CATOBAR carrier offers is the ability to launch a wider variety of aircraft types under a wider array of conditions than STOBAR carriers. One of the most significant additions are fixed-wing carrier-based airborne early warning and control (AEWC) aircraft. 

Presently, there is only one fixed-wing carrier-based AEWC in service in the world, the E-2 family. It was developed by the US company Northrop Grumman, and is operated by the U.S. Navy and several other nations. However, China is developing the KJ-600 (also known as H-600), a similar aircraft developed by Xi’an Aircraft Industrial Corporation (XAC) and 603 Institute. The KJ-600 first flew in mid-2020. 

This article will review the status of this aircraft, some of the common discussion points, and consider the future milestones it is expected to meet.

As of this writing (in early July 2023), it is thought that at least six KJ-600 prototype airframes are in various stages of testing. At least one of these is likely to be a static test frame, while the others are flying prototypes serving various roles. 

Notably, so far there has been no visual evidence (photo, video, or satellite) to suggest that KJ-600s have undergone catapult launch or arrested recovery testing from the land-based catapult test site at the PLAN Carrier Aviation Test and Training Base. However, it is also highly possible such tests have occurred without being captured, as a natural result of usual PLA operational security and the relative infrequency of satellite imagery overpass.

Overall, prototype flight testing continues, and the KJ-600 program is likely to be on the verge of low rate initial production, which would somewhat dovetail with the fitting out, and anticipated sea trials and aviation trials that CV-18 Fujian (Carrier 003) will undergo in the near future. 

Configuration and Subsystems

The KJ-600 adopts a configuration not dissimilar to other carrier-based fixed-wing AEWC types in recent history, most notably the E-2 family but also the proposed Soviet Yak-44, and the E-1 (predecessor to the E-2 family). It is a high-wing, twin turboprop powered aircraft, with tricycle landing gear where the rear landing gear is integrated into the engine nacelles. A distinctive rotodome radar is installed atop the fuselage. 

Based on satellite imagery measurement, the KJ-600 is estimated to have an extended wingspan of 24.4 meters and a length of 18.4 m, consistent with the compact dimensions expected for a carrier-based aircraft.

Recent high-quality imagery allows several features to be identified. The turboprop engines are six bladed, and highly likely to be the WJ-6C (a mature turboprop that has powered Y-9 derived aircraft for a decade and a half). A catapult launch bar on the nose landing gear confirms CATOBAR launch compatibility, and a rear Y-shaped recess in the rear fuselage and a small tailhook tip virtually confirms the presence of a Y-shaped tailhook for arrested recovery. A number of antennae can be identified on the ventral fuselage and also below the wings, as well as a rear box-shaped antenna below the rear. Wing fold lines are possibly visible, but at present, the KJ-600 has yet to be seen in a folded/stowed state.

The designation of KJ-600’s primary radar is not known, but it is expected to be an active electronically scanned array (AESA) type, which is considered a highly mature technology for the Chinese aerospace and avionics industry. The distinctive KJ-600 rotodome radar appears to be a single-sided array, based only one half of the rotodome possessing a gray dielectric cover. A rotodome radar configuration with a single-sided array is different from the tri-face fixed dome seen on other Chinese AEWC aircraft like the KJ-500 or KJ-2000. This may reflect a requirement that emphasizes greater array size (and thus output) over fixed 360-degree monitoring, which is not unreasonable given a carrier-based AEWC aircraft is much smaller than its land-based counterparts. The E-2 family also uses a rotating single sided array. It is not known which frequency band the KJ-600 radar will operate in, but given it is an AEWC aircraft, the L or UHF bands are most probable. 

It has been suggested this radar would be developed by the 14th Institute. Overall, based on the technological context and timing of its development, the KJ-600’s radar and overall avionics suite is likely to field the most recent and newest technological advances of the Chinese industry in domains such as materials, software, and upgradability. In addition to the primary rotodome radar, a large gray nose radome indicates the presence of a nose radar, but it is unclear if it houses merely a weather radar or a more multi-mission radar. 

Total crew size for KJ-600 is expected to be at least five strong, with a pilot and copilot and at least three mission console operators. However, the exact number of operators cannot yet be confirmed. 

KJ-600 and E-2 Similarities 

Perhaps predictably, since the KJ-600 emerged, one of the most common themes punctuating articles and discussions around the aircraft surround its similarities to the E-2 aircraft family. Such a trend is understandable when espoused by casual military aviation enthusiasts, due to the highly similar external configuration of the two aircraft. However, there are also implicit insinuations or even outright statements that the KJ-600 is derived from reverse engineering the E-2, or through espionage of the E-2, or both. 

Much of this discourse arises from the very similar gross configuration and airframes of the two aircraft. That said, a cursory glance at the two aircraft yields obvious external differences in fuselage diameter and geometry, tail configuration, nose and cockpit geometry, landing gear height and detail, as well as other differences in overall dimensions, and nuanced positioning of key external features. The totality of these differences make it unlikely that the KJ-600 was reverse engineered or derived from the E-2 in the manner that say, China’s J-11B was from the Soviet Su-27. Indeed, if schematics of both aircraft could be attained, it is likely that there would be differences in the cross-sectional plans between both aircraft. 

The similar configuration between the KJ-600 and E-2, is undeniable, but this is not particularly scandalous. After all, the same basic configuration was arguably first fielded by Northrop Grumman in the E-1 in the mid-1950s, who refined it to its present E-2 form in the 1960s. It was also investigated and developed in the late cold war by Yakolev in the form of the Yak-44, before Xi’an adopted the configuation in 2020. Such parallels are fairly common throughout aviation history, seen in aircraft such as the B-1 and Tu-160; the Boeing 737 and Airbus A320 families (including modern variants); a number of stealth fighter aircraft (the U.S. F-22 and F-35, Chinese FC-31/J-35, Korean KF-21, Turkish Kaan, and Indian AMCA); or any number of recent flying wing unmanned combat vehicles (including but not limited to the Phantom Ray, GJ-11, Neuron, Taranis, Anka-3, and Okhotnik-B).

On the other hand, the configuration of the KJ-600 is an excellent example of PLA pragmatism, which has been one of the defining characteristics of many of its military projects since the 1990s (and arguably, one of the contributors to the relative success and speed of PLA modernization during the last two decades). It is likely that requirements for a fixed-wing carrier AEWC were first laid out in the early 2010s, and different configurations and powerplant choices would have been assessed. However, powerplant options would have been the most significant limiting factor for the Chinese aerospace industry at that time (and is still the case now). 

For example, the U.S. Navy considered a jet-powered successor to the E-2C (and other carrier-borne aircraft) called the Common Support Aircraft, before embarking to develop the E-2D Advanced Hawkeye instead. For the PLAN, no suitable jet engine was available for a fixed wing AEWC/support aircraft, and while development of such an engine was likely within the industrial capabilities of the aeroengine industry at the time, it would still require time, funding, and risk for a clean sheet powerplant to emerge from the drawing board to an acceptable state of maturity. Thus, it was good fortune that the WJ-6C turboprop was in a state of emerging maturity and appropriate in dimensions, output and weight class for a carrier based AEWC, and ultimately adopted. 

From there, it is likely that alternative airframe designs were considered, and the mature configuration in use for the E-1 to E-2, and pursued for the Yak-44, would have been viewed as the most mature and lowest risk option. Pursuing a proven configuration would still necessitate clean sheet structural design and engineering, as well as aerodynamic wind tunnel testing. Individual components such as fuselage structure, bulkheads, engines, landing gear, arresting gear, would all have to be designed, tested, and integrated for what would by definition be a clean sheet aircraft design. Arguably most importantly, the aircraft’s mission systems such as its radar, passive sensors, processors, mission consoles, datalinks, cockpit, and flight controls, would all need to be developed, tested and integrated as well.

Future Milestones, Potential Upgrades, and Variants

A number of developmental milestones remain for the KJ-600, and some of these are likely to only be confirmed retrospectively after they have occurred, due to PLA operational security. The aforementioned land-based catapult launch tests and land-based arrested recovery tests will be meaningful flight test milestones. After that will be carrier-based catapult launch tests and carrier-based arrested recovery tests, the latter two of which are likely to depend on the Fujian achieving sufficient readiness during its sea trials to begin aviation trials. 

A major unknown for the KJ-600 is whether it would be capable of launch from a ski jump (even if it were in a reduced fuel load state), which would allow the STOBAR carriers CV-16 Liaoning and CV-17 Shandong to test and operate the KJ-600. This possibility would greatly enhance the flexibility of the two STOBAR carriers as well as the KJ-600, but at this stage it is assessed as unlikely. 

Following completion of flight test milestones and carrier integration trials, entry into service would occur. This may potentially precede the commissioning of the Fujian as acceptance of the KJ-600 first could allow for pilot and crew training to commence so as to minimize “down time” before the Fujian becomes mission capable.

The service life of the KJ-600 is likely to span multiple decades, and upgrade packages are virtually guaranteed going forwards, especially for mission systems and avionics. One propulsion upgrade that has been rumoured is that a newer, more capable turboprop may be used for the KJ-600, potentially the AEP500/WJ-10, but this is yet to be confirmed. Other structural upgrade options include the addition of an air refuelling probe to extend mission radius and endurance.

The KJ-600 may also provide a viable basis for other aircraft variants. A carrier onboard delivery (COD) variant similar to the C-2 Greyhound has been rumoured as the most likely candidate, followed by an anti-submarine warfare (ASW) variant. However, these are unconfirmed and are not currently treated as anticipated. Additionally, as the KJ-600 is a relatively small-sized, twin-engine AEWC, the baseline aircraft may have promise as a relatively lower cost, but fairly advanced AEWC for other international customers that cannot procure a full sized AEWC aircraft.