What’s Wrong With The U.S. Navy’s F/A-18s?
Lara Seligman
The U.S. Navy flag officer leading an investigation into a spike in unexplained physiological events across the service’s fighter and trainer aircraft believes her team is turning the corner on finding a solution to the problem in the F/A-18 fleet.
But the Navy has a long way to go before pilots can climb into the cockpit without fearing potentially lethal changes in pressure or oxygen during flight.
The stakes are high for Boeing, which builds the legacy F/A-18A-D Hornet, the F/A-18E/F Super Hornet and the EA-18G Growler electronic-warfare variant, all of which have experienced a sharp increase in hypoxia-like physiological events (PE) in the last decade. During a Feb. 6 congressional hearing, Rep. Niki Tsongas (D-Mass.), ranking member on the House Armed Services tactical air and land forces subcommittee, stopped just short of calling for a production halt.
- A top lawmaker stopped just short of calling for halting production of Boeing’s F/A-18s
- The Navy believes it is “turning the corner” on the F/A-18 PEs
- The service will issue an RFP for a new F/A-18 OBOGS
- NASA report points out potential design flaws in the F/A-18 ECS
“As we sit here today, new F/A-18s are rolling off the production [line] at a cost of around $69 million per aircraft,” Tsongas said. “At some point, paying $69 million for an aircraft we know has serious problems with its life-support system has to be questioned.”
Tsongas called on the Navy and Boeing to make improvements to the aircraft “that make them safer for our brave men and women in the military to operate, because we know there are lives at risk.”
It seems the Navy is heeding her advice. Rear Adm. Sarah Joyner and her PE team currently believe hypoxia—defined as lack of oxygen to the blood—and decompression events are the two most likely causes of the recent PEs, according to Joyner’s written testimony. In response, the service is looking to make a series of design changes to the F/A-18’s Onboard Oxygen-Generation System (OBOGS) and Environmental Control System (ECS) that it hopes will make the aircraft safer to operate, Joyner said during the hearing.
After almost a year of work, the team is beginning to see signs that the modifications are working, Joyner says.
“On F/A-18s, we are turning the corner,” Joyner told the subcommittee. On the sidelines of the hearing, she told Aviation Week: “We are going after the ECS to make it as steady as possible. We are going after the oxygen system to make sure we understand exactly what is going on. . . . PEs are not going to go away, but we are going to try to do our best to mitigate them and make them mild in nature as best we can.”
Most notably, the Navy intends to issue a request for proposals (RFP) to industry in the near future for a new F/A-18 OBOGS, Joyner confirms. The current version is built by Cobham. In particular, the Navy wants to replace the concentrator, the heart of the system, to conform to the latest MIL-STD 3050, Joyner tells Aviation Week.
She wants the new F/A-18 OBOGS to adopt some of the features of the F-35 system, built by Honeywell, including inlet/outlet pressure and data monitoring, she says. She could not provide a time line for release of the RFP.
The Navy has also redesigned certain internal components of the existing OBOGS to provide an improved filter and to incorporate a catalyst that will prevent carbon monoxide from reaching the pilot, Joyner stated in her written testimony. These new components have been installed in 92% of the in-service F/A-18 fleet.
A NASA team looking into the PEs pointed out in its recent comprehensive report that the existing OBOGS was originally qualified and accepted with “dry air under steady-state flow conditions,” which generally does not reflect actual flight operating conditions. The Navy intends to continue testing the OBOGS in realistic, off-nominal conditions, but Joyner tells Aviation Week that previous such tests have failed to make the system perform in an unsatisfactory manner.
“We’ve baked it, cooked it, soaked it, done tremendous badness to this concentrator, and we haven’t managed to make it really perform poorly,” Joyner says.
In addition to the OBOGS issues, the NASA report pointed out potential design flaws with the ECS, which is essentially the air-conditioning system of the aircraft. A problem with the F/A-18 breathing gas system as a whole is that the OBOGS gets fed last, according to the report. The enormous amounts of cooling air required for avionics and radars (particularly on the Growlers) means that the ECS controls “preferentially direct flow to them,” it concludes.
This is a particular problem for the newer Super Hornets and the Growlers, which have substantially larger demands for airflow than legacy aircraft, due to the sheer amount of electronics stuffed onto the airframe. Despite the increased demand for cooling air, key ECS components and primary ducting systems are essentially unchanged, the NASA team writes.
They also pointed out that significant changes in cabin pressure can occur due to the way the Cabin Pressure System is designed. There is no active pressure control in the cockpit, and there is a general lack of data about how the ECS performs in a real-life flight environment, according to the report.
Further, the Navy appears to have little insight into elements of the ECS control programming logic, because this information was not part of the original contract deliverable for the F/A-18—which was first fielded in the 1980s—“and therefore may no longer be documented in any form,” the NASA team writes.
Joyner disagrees with the NASA conclusion that the ECS controls preferentially direct flow to the avionics over the OBOGS. However, she agrees that the Navy needs to better regulate the ECS to ensure steady airflow.
The service is implementing eight “corrections” to the ECS to try to “smooth the flow,” she told the subcommittee. Meanwhile the legacy Hornets are undergoing a phased ECS overhaul, which will include replacing several critical components such as valves, duct lines and brackets. In addition, the Navy is working with Boeing to upgrade the ECS software on the F/A-18 and EA-18G Growler to mitigate fluctuations in cabin pressurization due to moisture freezing in the system’s piping, Joyner says.
The service also intends to develop and install a new system to monitor cabin air pressure and alert the pilots to any abnormalities as well as to replace the F/A-18’s cabin pressure regulator valve, Joyner confirmed during the hearing. Right now, aircrew carry “SlamSticks,” small pressure recording devices, on all sorties to help investigators track and collect cabin pressure data.
The Navy has constructed an ECS laboratory to further investigate the issue, according to Joyner’s testimony.
She cited the success of the changes the Navy has made to the T-45 Goshawk trainer as reason for Congress to have confidence in the PE team’s approach to the F/A-18. After a similar cluster of PEs caused the service to ground the Goshawk fleet in April, the T-45s are now fully operational, Joyner says.
The U.S. Navy’s legacy F/A-18A-D Hornet, F/A-18E and F/A-18E/F Super Hornet and the EA-18G Growler electronic warfare variant, the backbone of naval aviation, have all seen a sharp increase in hypoxia-like physiological events in the last decade. Credit: Seaman Ryan Carter/U.S. Navy
In addition to updating maintenance and cleaning procedures for the T-45’s OBOGS, the PE team also installed new sieve beds—to filter out contaminants—and a new water separator, and incorporated a carbon monoxide catalyst, according to Joyner’s testimony.
The Navy also fielded new CRU-123 solid-state oxygen-monitoring units, which alert aircrew of changes in delivery changes. This ability to log data has provided “invaluable” insight into the performance of the T-45 oxygen system and given aircrew “new confidence,” Joyner says. As of Jan. 24, a total of 163 new oxygen monitors have been installed.
The Navy has also released a draft RFP for a new T-45 oxygen concentrator, dubbed the GGU-25, which will be a “significant increase in capability” over the 1980s-era system the aircraft now uses, she adds.
“We have turned the corner on [the] T-45,” Joyner says. But “we are not declaring victory. We have a Root Cause Corrective Analysis team that goes line by line, starting with the human, ending with the human, trying to find the root cause for both the T-45 and the F/A-18 [PEs].”
The Navy plans to install an automatic backup oxygen system on the T-45, but it has no plans to install a similar system at this time on the F/A-18, Joyner confirmed in response to questions from Tsongas.