Main image caption: C-47TP ‘6885’, one of five operated by 35 Squadron South African Air Force in the maritime surveillance role. Built in 1944, it’s now an incredible 73 years old. Photo by Alan Wilson

All eight of the South African Air Force 35 Squadron’s C-47TP transport and maritime surveillance aircraft were grounded for much of 2016, leaving a severe gap in the country’s coverage of its oceans.

The C-47TP, also known as the ‘TurboDak’, is the result of an upgrade of the venerable C-47 Dakota, under Project Felstone with modern PT-6A 65R turboprop engines, updated avionics and a lengthened fuselage to adjust for the change in centre of gravity brought by the lighter engines. At least twelve C-47s were converted between 1989 and 1994, with 35 Squadron being the only unit to operate them.

Although upgraded, many of the C-47TPs are over 70 years old, making them some of the oldest military aircraft in active service anywhere in the world.

Their extended grounding was related to two separate technical issues: An unspecified but reportedly minor issue with the aircraft undercarriages, and a need to replace the primary flight control cables in response to a Australian Civil Aviation Safety Authority (CASA) airworthiness directive (AD) AD/GENERAL/87.

That directive requires the removal and destruction by 1 January 2018 of all primary flight control cables that use terminals constructed of SAE-AISI 303 Se or SAE-AISI 304 stainless steel and are either more than 15 years old, or of unknown age in aircraft built before 2003. This is as a result of widespread stress corrosion fractures discovered in aircraft control cables older than 15 years across Australia, New Zealand, the United States and the European Union in the past few years.

No less than 61 primary flight control cable corrosion discoveries and 4 outright cable separations have been recorded in Australia alone since 2012, with similar numbers seen in other countries. Most of these were discovered on the ground, usually after pilots reported unusual control feedbacks, but some in the United States caused severe or even fatal accidents.

Terminal cracking and surface corrosion shown on a control cable assembly. Source: CASA SDR 510004928 (via NPRM 1303 MS)

Metallurgical analyses of failed assemblies showed that cracking could originate from within the sleeves of the terminals before becoming apparent on the outer surface, although it and other stress corrosion failures were correlated with some surface corrosion. This mean that in-place visual inspections of the assemblies alone would be insufficient in identifying stress corrosion.

Nonetheless, it’s unusual for an AD to specify the complete removal and replacement of components, as in most cases it’s sufficient to mandate that items are inspected either visually or through some other non-destructive inspection (NDI) technique like dyes or x-rays, but after conducting numerous tests CASA discovered that neither visual nor NDI techniques were sufficient to identify whether an assembly had stress corrosion. Dye-penetrant NDI was abandoned, as none of the readily-available dyes provided sufficient guarantees. Eddy current NDI was considered unreliable owing to the cable geometry and the type of corrosion. X-ray NDI was similarly constrained by the cable geometry, as well as high cost and the lack of a readily-available procedure.

A cross section of a failed control cable, showing cracks propagating from inside the terminal sleeve. Source: NZ CAA (via CASA NPRM 1303 MS).

The only inspection method considered suitable was the complete removal, disassembly and cleaning of each control cable assembly followed by a visual inspection at 10x magnification. CASA thus issued a notice of proposed rule-making, NPRM-1303MS, which presented for comment the option of mandating either the removal, disassembly and inspection, or the complete removal and replacement, of control cables. Responses from the public and general aviation industry indicated that as both options would result in a similar labour cost the outright replacement was the more pragmatic approach.

Even though the South African Air Force is not bound by Australian ADs in any way, it maintains its own airworthiness directorate and adopts foreign ADs that might apply to its aircraft. In the case of the C-47TPs, the aircraft’s maritime role means their components are more prone to corrosion than most and so out of an abundance of caution the organisation decided last year to adopt AD/GENERAL/87 as an internal directive.

However, it’s unclear why the process of removing and replacing the primary flight control assemblies on the South African Air Force’s C-47TPs took such a long time to complete. While the Air Force has declined to provide details, some analysts have speculated that the cause may be either a shortage of sufficiently-qualified manpower, or the bureaucracy and red tape around acquiring new assemblies, having them fitted, and signing off the work.

Whatever the cause, by February this year the process was complete and the C-47TPs returned to the sky, with aircrew conducting training flights throughout March to regain operational competency and currency. As of the time of writing, the aircraft are once more on operational patrols.

A complete terminal failure shown. Source: CASA SDR 510009411 (via NPRM 1303 MS)

There is an almost impossible burden placed upon 35 Squadron, the Air Force’s sole maritime patrol unit. Only five of its eight C-47TPs are configured for the maritime patrol role (two are transports and one is a dedicated airborne Electronic Warfare testing and training platform) and their operating budget is so low it’s amazing they’re able to keep any aircraft flying let alone most of their fleet.

35 Squadron has a long and rich heritage of maritime patrolling, having operated Catalina and Sunderland flying boats until 1957, followed by the magnificent Shackleton MR3 until 1984 after which it received a fleet of C-47s. In December 1990, 25 Squadron and 27 Squadron were shut down and their personnel and aircraft moved into 35 Squadron, giving it a secondary transport role that it retains to this day.

In addition to the basic maritime surveillance and transport roles, 35 Squadron is required to perform a diverse set of missions such as search and rescue, paratrooping, target-towing, CASEVAC, electronic intelligence gathering, tactical photographic reconnaissance, and training for new navigators and radio operators.

With its maritime-configured C-47TPs, which fly with a crew of 10, the squadron is expected to not only patrol the South African coastline and EEZ, but also to perform anti-piracy patrols of the Mozambican Channel as part of Operation Copper.

According to an article by Dean Wingrin, these ongoing 35 Squadron patrols of the Mozambican Channel are performed via an elaborate ‘airport hopping’ mission from their home base at AFB Ysterplaat in the Western Cape. A typical sortie would begin with a flight from AFB Ysterplaat to AFB Waterkloof in Pretoria, then on to Maputo, Beira, and Pemba for patrols before returning back via the same route. On the legs between Maputo, Beira, and Pemba the aircraft will patrol inshore all the way to the Ruvuma River, spending most of its time in the area between Pemba and the Comoros before patrolling shipping lanes out to 60 nautical miles.

Previously, 35 Squadron had a C-47TP deployed permanently at Pemba in support of the Copper patrols, but the cost of sustaining a detachment there prompted the change to a new approach as the piracy threat decreased.

When one considers that the C-47TP is unpressurised, has a range of only 2 800 km and is not equipped with any advanced sensors such as 360º maritime search radars or FLIR turrets, it’s remarkable how well the squadron is able to perform its many diverse tasks day in and day out. Like so many other units in the South African Air Force, their persistence in the face of adversity is admirable.

However, it’s clear that this situation cannot last, and that 35 Squadron needs both new and more capable aircraft and significantly more funding if it is to be able to truly patrol not only the country’s EEZ and coastal areas, but also Prince Edward and Marion Islands where much illegal fishing activity takes place.

A replacement for the C-47TP has been on the cards for over a decade and has gone through at least two procurement attempts that failed to yield results. Project Saucepan, which envisioned the acquisition of a single type to replace both maritime patrol and light transports, was cancelled after languishing for many years and replaced by Projects Metsi, for a new maritime patrol aircraft to replace the C-47TPs in the maritime role, and Kiepie, to replace the transport-configured C-47TPs and the C-212s. But both of these projects remain unfunded and have been for years, with no immediate sign of movement in the near future as a result of the overall SANDF budget crunch.

An interesting proposal from a South African consortium led by Atlantis Aviation, to provide Dornier Do-328s fresh from a search and rescue contract with the Australian government, was presented to the Department of Defence last year but turned down for unspecified reasons.

Although last year’s grounding of the C-47TPs was not specifically related to their age, it’s a timely warning for anyone watching that the resources allocated to airborne maritime surveillance of South Africa’s waters is wholly inadequate and that the C-47TPs are old and will only experience more component issues as time goes on.

Note: This article appeared in the May 2017 issue of FlightCom magazine. It is republished here with that publication’s permission.