They stated that the seats were only rated for 110 kg (240 lb), not considered enough for a fully equipped soldier. Heavy infantry weapons could not be adequately secured and the cabin floor was prone to damage, citing an anecdote of damage caused by footwear. The helicopter could only land on firm ground, with obstacles not exceeding 16 cm (6.3 in). Troops carrying full equipment could not use the rear ramp due to weight-limitations placed on it. Adding a door machine gun was not possible due to space taken by troop ingress and egress; there was also no provision for fast roping or paratroop equipment. In response, the German Defense Ministry proclaimed that this article referred to a prototype, not to the production model; the specifications for which were not even finalised at the time. The prototype evaluation and its results were described as a normal procedure in an ongoing design process. In November 2011, the MRH90 program was placed on the Australian Department of Defence's "Projects of Concern" list. The most serious problem identified by a diagnostic review, which caused a brief grounding in 2010, is compressor blade rubbing caused by the bending of a spool in the Rolls-Royce Turbomeca RTM322 engine due to uneven cooling after shutdown. Other problems identified include failure of transmission oil cooler fans, windscreen cracking, an inertial navigation system that is slow to align, and the weakness of the cabin floor to withstand the impact of soldiers’ boots – a problem also encountered in German service. In March 2014, it was announced that a Dutch NH90 had suffered higher than expected fuselage wear and corrosion following an extended deployment at sea; analysis by the Dutch National Aerospace Laboratory attributed the corrosion to design and assembly flaws. In response, NHI Industries launched a corrosion prevention programme and enacted several design modifications. In December 2014, Dutch NH90 deliveries, which had been temporarily halted earlier in the year, restarted after the majority of identified points were addressed and an agreement was made by the manufacturer to bear the cost of developing modifications, repairs, and preventive measures against corrosion. The operating cost of a NH90 HCV (High Cabin Version) was estimated at 200,000 SEK per hour flown, or about US$24,000, in 2018. The NH90 was designed to fulfill a NATO staff requirement for a multi-role, medium-sized military helicopter for both land and maritime operations. According to Flight International, the NH90 has the distinction of being the first helicopter in the world to be developed in line with NATO requirements.