In The Netherlands, Australia’s Blackhawk replacement is corroding at the seats

Ruben Veenstra for Veenstra & De Vries Aviation Publishing

On 7 July we reported on Dutch Defense Ministers Hennis-Plasschaerts decision to freeze the acquisition of the European made NH-90. The DM made her decision after the Dutch Aerospace Laboratory released a report on design and manufacturing errors causing heavy wear and corrosion on the Dutch NH-90s. It’s not the first time the NATO Helicopter has suffered from these kinds of problems as the Australians have had similar experiences.

According to an Australian Defense spokesperson, “Australia’s MRH-90s (Australia’s designation of the NH-90, Ed.) have experienced higher-than-anticipated corrosion.” The country conducted a “Corrosion Based – Reliability Centered Maintenance study of the MRH90” in 2009-2010. Although the report is not publicly availably, the spokesperson told us that some parts of the aircraft were vulnerable to corrosion and measures had to be taken. A 2013-2014 performance audit on the Multi-Role Helicopter program, citing the same study, revealed that corrosion had already taken place prior to delivery of the aircraft.

The MRH-90 is the Australians replacement for their ageing fleet of UH-1 “Hueys” and S-70A-9 Black Hawks of the Army branch. Around 2005 several contractors offered bids for a new fleet of helicopters. Among them Sikorsky with a new variant of the Black Hawk. The Australians opted for the cheaper but immature NH-90 instead. Of the total ordered, 40 will go to the Army and six are assigned to the Navy.

To get a glimpse into the problems relating the MRH-90 we turn back to the Dutch NLR report because it gives a very extensive list of failures on behalf of the manufacturer NHIndustries. The researchers often point to galvanic coupling as a reason for the corrosion on parts of the NH-90. Galvanic coupling, or galvanic corrosion, occurs when two different metals get in contact while an electrolyte like salt water is present. The Dutch operate the Naval Frigate Helicopter. As its name implies this type is designed with a specific task set in mind, namely being deployed on ships at full sea so salt water is around in abundance.


Galvanic coupling can be reduced for example by applying grease to the metal in order to prevent contact with salt water. Another method is to add insulation in order to avoid contact between the metals altogether. As the researchers found out these basic measures where at times poorly executed or otherwise not applied at all. Take the inside of the main sliding door: it was not coated with a primer to avoid corrosion while it would inevitably be exposed to salt water when flying with the door open. In another example, the aluminum floor panels are in direct contact with the fuselage. So when the paint inevitably scuffs it will come in direct contact with salt water and corrosion will occur through galvanic coupling.

Another cause of corrosion is stagnant salt water. The NLR had to advise adding drainage holes in order to expel water from the fuselage and tail. In a case where a drainage hole was present in a part of the tail, the hole wasn’t at the lowest point unless the tail was folded thus allowing salt water to accumulate.

The cockpit area wasn’t safe from corrosion either. Bare steel parts and pins of the pilot’s seats were rusting away. Even the metal parts on the dashboards were corroding because the manufacturer didn’t account for the salt-water spray getting in the cockpit when flying with the sliding door open.

It is important to note that the Dutch operate the Naval Frigate Helicopter version for use at sea and the Australians the Troop Transport Helicopter. The Australian spokesperson estimated that “each MRH-90 will operate in salt-water environments less that one-fifth or their total life (expressed in flight hours).” That’s not a whole lot. And still these helicopters had corrosion problems. Imagine how bad the problems could have been if the aircraft would have more flight hours in salt-water environments.

In all fairness, corrosion is not a problem specific to the NH-90. Any aircraft deployed at sea will have corrosion problems at some point. But these problems can be prevented or at least be reduced. These measures were not always applied when the NH-90s where delivered.

When we asked NHIndustries for a response on the report, the Dutch decision to halt deliveries and if the report will result in adjustments to their quality assurance programs, NHI spokesperson Patrick Brunet declined to comment in detail but added that “we at NHI dedicated a task force in cooperation with the Dutch customer in order to solve these issues. I.e. analyze the root causes and define and implement the appropriate preventive and corrective measures.”

The tides seem to be turning in favor for Sikorsky. Although the Army passed Sikorsky, the Australian Navy is acquiring Sea Hawks to be flown in 2018. Reportedly delivery problems and delays around the MRH-90s weighed in with the decision to opt for Sikorsky’s helicopters. Other countries are joining the ranks as Denmark has gone for the mature Sea Hawk in 2012. And just recently voices within the Dutch military community are pushing for buying second hand Sea Hawks because of their problems with the NH-90 and the heavy pressure on the few remaining helicopters the Dutch military has. Countries are playing it safe: they are going for off-the-shelf rather than new and unproven. If these acquisitions are any indication, it looks like the aircraft manufacturers are going to do business with their existing aircraft for quite a while longer.