‘Engine corrosion' grounds large numbers of Japan's home-grown P-1 patrol aircraft

Straits Times

30-06-2025

Japan's P-1 patrol aircraft has encountered issues such as engine corrosion and intelligence-gathering equipment failures, the Board of Audit has found. PHOTO: JAPAN MARITIME SELF-DEFENCE FORCE
– Japan's P-1 patrol aircraft, a proud symbol of domestic innovation as its first home-grown maritime reconnaissance plane, is 'woefully underused' due to engine corrosion and intelligence-gathering equipment failures, the country's Board of Audit has found.
In a searing 38-page report on June 27, auditors highlighted a litany of defects that could have been prevented during the aircraft's development. It also blamed delays in securing replacement parts on a lack of proper judgment.
The Defence Ministry said it took the findings seriously.
'Many P-1 aircraft were not in a state where all equipment were functioning properly and could be used for missions without restrictions,' the report said.
'Yet, the P-1 plays an important role in securing Japan's national interests, with flight patrols over territorial waters, and smooth passage of vessels through its sea lanes.'
The revelation exposes a potential chink in Japan's maritime surveillance armour as China escalates its activities in the high seas sometimes close to Japan's outlying islands.
It also underscores the challenges that Japan faces in its efforts to fire up its national defence industry, which has atrophied due to low profitability during a half-century of weapons export ban that has gradually been eased since 2014.
The auditors launched an ad hoc probe into the P-1 since a 'large amount of national funds has been invested in its development'.
The audit also came after the 2023 Defence White Paper cited the P-1 as an example of a military unit that has been crippled by a lack of parts.
Japan spent 1.78 trillion yen (S$15.7 billion) on the research, development, procurement, maintenance and repair of the P-1 from 1991 to 2023, the audit board said.
The P-1 has been globally recognised for its submarine detection prowess, and holds the distinction as the world's first aircraft with a fly-by-optics system. This transmits control signals from the cockpit via optical fibres instead of electrical wiring, making planes lighter.
Japan decided to make its own patrol aircraft as a successor to its P-3C Orion aircraft made by America's Lockheed Martin.
Kawasaki Heavy Industries is manufacturing the P-1, using F7-10 turbofan engines from IHI Corporation.
The P-1 was first deployed in 2013, and the Maritime Self-Defence Force (MSDF) now commands a fleet of 35 P-1 aircraft, and plans to add another 26 aircraft by 2054, for a total cost of 4.09 trillion yen.
The P-3C, in use since 1983, is gradually being phased out. The MSDF had 32 P-3C aircraft in operation as at March 2024, down from a peak of 98.
The fleet of 35 P-1 aircraft, whose maximum speed of 830kmh makes the aircraft 1.3 times faster than the P-3C, is strategically stationed at three MSDF bases: Kanoya in Kagoshima in south-western Japan, as well as at Atsugi and Shimosa to the south and east of Tokyo respectively.
The P-1 is equipped with, among other things, sonar and electromagnetic radars to detect submarines.
The audit report described the operational status of the P-1 from 2019 to 2023 as 'subdued', without specifying the number of aircraft that were being grounded and the types of intelligence equipment that glitched, given that this could 'jeopardise national security'.
Professor Heng Yee Kuang of The University of Tokyo's Graduate School of Public Policy told The Straits Times: 'The Kawasaki P-1 is one of the 'crown jewels' of Japan's kokusanka policy to build self-reliance in its domestic defence industry by utilising path-breaking technologies.'
He added that the report spotlights the dilemma facing Japan's defence planners: how to balance wear and tear on its limited assets and manpower against the need to maintain persistent and continuous surveillance of Chinese and Russian maritime activities.
'This is a reminder that military operations remain critically dependent on logistical nuts-and-bolts issues, which are often unglamorous,' he said.
Maritime patrol planes fly for prolonged periods at low altitudes over the high seas to monitor foreign submarines and suspicious ships.
But the P-1 was vulnerable to salt content in the air that led to engine corrosion, thus 'rendering a certain percentage of engines permanently unusable', the report found.
While the problem was discovered during the development phase, based on test standards used by the US military, these test conditions were changed under the pretext that the 'expected operations are different'.
When the same problem was found during operations, IHI brushed it away as an 'accidental occurrence' – an explanation that the ministry accepted.
A proposed fix for the engines to be thoroughly scrubbed down with pure water after each flight was not carried out as it was 'too onerous' on servicemen.
As for malfunctions of electronic equipment, this could have been prevented with more rigorous stress-testing during development, the report said.
The MSDF Air Supply Depot was also too overoptimistic over the procurement of replacement parts, the report added, noting that only 30 per cent of spare parts could be delivered within a year of a request being made.
The chronic shortage, blamed on a global semiconductor shortage and supply chain issues, has meant that 'cannibalistic maintenance' was necessary by replacing parts of one P-1 unit with those from other P-1 aircraft .
Still, experts noted that many modern military aircraft such as the F-35 stealth fighter jets have been plagued with teething problems, which makes the P-1's woes not extraordinary in the broader context.
'It is important that Japan grows its military self-reliance especially to prepare for a crisis – until now, there has been no motivation to grow its defence production lines because Japan's Self-Defence Forces were the only customer,' said non-resident fellow Satoru Nagao of the Hudson Institute, a US think-tank.
'But given Japan's lack of field experience after World War II, it suffers from many blind spots,' he added.
Yet, to make the industry viable through export, it will be important for Japan to win customers among like-minded militaries abroad.
Prof Heng said given that Japan has been trying to sell the P-1 to the Italian Navy, the bad press came at an inopportune moment.
'The Defence Ministry will have to demonstrate its ability to iron out these maintenance problems to convince would-be buyers,' he said.
Walter Sim is Japan correspondent at The Straits Times. Based in Tokyo, he writes about political, economic and socio-cultural issues.
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