The US Navy is still struggling to find the root cause of the hypoxia issue plaguing the F/A-18E/F Super Hornet and E/A-18G Growler, service leadership told House Armed Services Committee members this week. The service’s Boeing F/A-18s are experiencing a dangerous crew cabin pressure issue, while the newer variants may have possible oxygen contamination.
Since 2010, the Navy has directed pilots to report possible symptoms that could be related to the Super Hornet’s onboard oxygen generation systems (OBOGS) and environmental control system (ECS). Lawmakers expected hypoxia rates to increase once pilots became aware of the issue, but were still surprised at the uptick in physiological events. The F/A-18A through D models saw a 90% increase in physiological episodes (PEs) in Fiscal 2016 compared to 2015, while the E and F models saw an 11% increase in the same period. Meanwhile, the EA-18G Growler doubled its number of PEs during that same time, according to information delivered to Congress by the navy.
Over the last year, the Navy has developed protocols to review each ECS component on a malfunctioning F/A-18, Director of navy tactical aircraft Rear Adm Michael Moran told lawmakers during a 28 March hearing. Some aircraft with persistent problems were transferred to Naval Air Station Patuxent River for further inspection, he says. The Navy has determined that rather than repair valves and switches as they fail, the service will replace parts for the legacy Super Hornets on a schedule now known as the ECS reset.
The US Navy is also taking part in an investigation into an air contamination incident on an Australian Air Force F/A-18. During that incident, both the pilot and ground crews who sat in the aircraft’s cockpit and breathed air from the system experienced dizziness and degraded cognitive ability for a half hour. The navy suspects lubricants and engine fluids might have seeped into the oxygen generation system, though the process is not fully understood.
The Navy observed a grease lubricant on the nose wheel well contributed the most contamination and has since told the service to control the amount of grease applied to the wheels, Moran says. That’s a potential cause, but the navy did not see enough numbers of incidents to identify its effects on humans, he adds.
“Also for that process there’s fluid for the radar cooling and so there’s a discharge port that basically could release some contaminants into the engine, because the engine is ingesting air all around the airplane,” he says. “We’re looking really hard at everything possible the engine could ingest and contaminate the air we’re breathing.”
The Navy still isn’t sure why the Growler experienced a higher PE event rate over other F/A-18 variants, though Moran points out the EA-18G’s electronics put a greater strain on the ECS system. Boeing will examine one of the Growler’s ECS systems and the Navy has already changed a restrictor plate on the aircraft to increase the airflow to the avionics that helps control its pressurisation issues, Moran says.