Hyd games over the South Pacific.
Because I had "popped" on the schools list, I would be leaving deployment early to return to CONUS, check out of MCAS Miramar, and move my whole life to Quantico, Va., where I would be attending Command and Staff College. I was nearing the end of an unforgettable three-year tour with the Black Knights of Marine Fighter Attack Squadron 314. Having spent my previous two years as the AMO and OPSO, I was enjoying life as a pilot for my last month in the squadron. The Black Knight's trusty stable of Lot 8 and 9 FA-18A++ aircraft had been performing well, and I'd been flying my share. I would make the push to Australia, have a few days with the bros, and then hop a commercial flight to the States.
The squadron had just wrapped up nearly three months of hard flying out of Kadena Air Base in Okinawa, Japan, culminating with our participation in MAWTS-1's MDTC (Marine Division Tactics Course). The plan was for the skipper to lead the first cell of six jets, and I would lead the second cell of five jets (one plane was hard down and remained in Kadena with a small repair det). The TransPac plan had us flying to Guam, where we'd spend the Fourth of July weekend. We'd then press on to Townsville via some circuitous routing through the islands of Indonesia. We had to avoid the overflight of any land mass for diplomatic-clearance restrictions.
The tanking plan was to have one KC-10 per cell to Guam, and then one KC-10 and two KC-135s per cell from Guam to Townsville. This creative routing makes for an eight-hour flight. We also had an Air Force C-130 hauling our trail maintenance folks along with the parts pack-up. Finally, we had a squadron pilot riding along in each KC-10, with a NATOPS manual, to act as a book reader in case of an emergency.
The flight to Guam from Kadena was uneventful with the exception of my cell having to slide 24 hours to the right because of maintenance issues. The skipper's cell made it out of Guam on time, but my cell had to slide yet again because several jets didn't want to cooperate. Three days and one frantic parts run later, my cell launched from Anderson AFB, Guam, for the almost 3,500-mile trek to the "Land Down Under." I would land in Townsville with enough time for a last flight with the squadron in Australia during the range-familiarization day. The multiple slides had ended that plan, and my last flight before checking out of the squadron would now be this joyous eight-hour leg to Townsville. At least that was how it was supposed to go.
The first few hours of the flight were routine. Everyone was handling the Iron Maiden quite well. We were to tank off of the KC-135 for the first few aerial refuelings (ARs), and then detach him so he could head back to Guam. The much easier-to-deal-with KC-10 would drag us the rest of the way to Townsville and then to Darwin International.
I kept busy during the flight by continuously tracking our diverts and making sure the fuel plan was tight. We were in and out of the clouds for the middle hour or two, but we mostly enjoyed a beautiful day in the South Pacific. I allowed myself to occasionally daydream about the tall glass of Victoria Bitter I'd have while scouting the local bar scene. We were about 50 miles from the point where our divert in the southern Philippines would roll forward to make Darwin our primary emergency divert. That's when I got the "deedle, deedle."
"What have we got here?" I wondered. The master-caution light was staring at me, along with a HYD 1A caution (indicating a problem with one of the four redundant hydraulic circuits) on the left digital-display indicator (DDI). I had briefed our cell about how we'd treat "land as soon as possible" and "land as soon as practical" emergencies. As the flight progressed, I'd call out where our land as soon as possible divert was as it changed. After breaking out the pocket checklist (PCL) and conferring with the rest of the flight, I decided to press forward toward Darwin and monitor the situation.
There were no associated flight-control system (FCS) Xs or BLINS (codes which explain exactly what component is having a problem). In the Hornet, the HYD 1A caution tells the pilot that the individual circuit pressure is below 1,500 PSI. This is what happens when a leak occurs and the HYD 1 fluid reservoir is down to 60 percent of full. This can also happen if the HYD system is not serviced properly between flights. The corrective action directs the pilot to simply maintain airspeed below 350 knots and to land as soon as practical. If the reservoir level-sensing (RLS) system has done its job, the leak will be isolated and there is no degradation to the aircraft's flying qualities. At this point, we were 400 miles north of Darwin, which equates to about 48 minutes of flying time.
About 15 minutes later the HYD 1A caution disappeared and was replaced by a HYD 1B caution. This means that the RLS could not isolate the leak in the HYD 1A circuit and the HYD 1 reservoir is down to 32 percent of full. The system shuts off the HYD 1B circuit to try to isolate the leak. We were a little more than 30 minutes from Darwin, still our closest divert. As a flight we discussed the procedures and worked crew resource management (CRM). My senior section lead backed me up with the notes. I was still in a land-as-soon-as-practical situation, and I still needed to remain below 350 knots.
I read ahead to the combined HYD 1A/HYD 1B procedures. If the RLS doesn't isolate the leak, once the reservoir is down to 4 percent of full it turns back on both systems and displays no cautions. In this scenario, you will likely be forced to shut down the corresponding engine, as the HYD pump is spinning with little to no fluid in it and poses the risk of a fire. The HYD pump is mounted on the airframe-mounted-accessory drive (AMAD), which is in turn powered by the rotating left engine; you would subsequently have no HYD 1 system. In this case, the aircraft had little degradation to basic flying qualities as everything was run by HYD 2 via the right engine.
The HYD 1B caution remained until we were about 10 miles north of Darwin. Our cell discussed the merits of landing in Darwin, or perhaps flying another 150 miles to RAAF Base Tindal (for possible Aussie RAAF Hornet support).
This scenario raised the question of what exactly "land as soon as practical" means? NATOPS states, "Land as soon as practical means extended flight is not recommended. The landing site and duration of flight is at the discretion of the pilot in command." This statement gives us a lot of latitude.
I considered pressing to Tindal for Hornet support, as I wrestled with the thought of whether the RLS would isolate the leak for me. A better call was to divert into Darwin, a field that would have me on deck about 20 minutes sooner than going to Tindal. The jet then decided to jump in and make the decision easy for me. After another "deedle, deedle," the left DDI showed the following cautions: HYD 1B, HYD 2A, FLAPS OFF, RUDDER OFF, FCS. I confirmed that I was more than 300 knots per the immediate-action item required for the FLAPS OFF caution.
The briefed plan was for me to take Dash 2 with me if I had to divert. We split-off from the tanker and once again started the checklists. I declared an emergency and began to coordinate our landing in Darwin. We stayed up the tanker frequency to have our book reader back us up with the big NATOPS. ATC was busy and our situational awareness (SA) was degraded; we had too many people talking on both radios.
My wingman and I pushed off to another tac freq where we could go through all the procedures. Both of my leading-edge flaps were X'd out, along with my right rudder. When you look at the Hydraulic Subsystems Malfunction Guide in the PCL, you find this is exactly what you'd expect to see. The big-picture game plan is to make a half-flap, straight-in approach to an arrested landing, after conducting a controllability check at altitude.
My wingman and I did a good job with the CRM as we set up for the visual approach. Darwin has only one runway to land on (the big runway is 11,000 feet with BAK-12s on either end, the small runway is 5,000 feet with no gear). I reviewed the emergency-landing-gear-extension procedures, while I had him check the limitations on the BAK-12. He came back with 160 knots; shouldn't be a problem. I told him to plan on pushing ahead of me and to land first, as I had no idea how long I'd have the runway clobbered after my trap. He helped me review the notes, and we confirmed the hook skip game-plan. I decelerated to 160 knots at 15,000 feet, and put the flaps to half to facilitate the emergency-gear extension and the controllability check. The nose and right main gear immediately came down.
What probably took only a couple extra seconds--but seemed like an eternity--was the left main gear showing down and locked. The hook was down and everything looked good. On the approach frequency, I heard a couple of international flights inquiring as to how long the runway would be down after my trap. They were concerned with holding time and divert fuel.
WITH ALL CHECKLIST ITEMS COMPLETE, the jet flew just fine. I descended to set up for a 10-mile visual straight in. As I took a quick inventory of the left DDI, I noticed the HYD 2A caution was gone, the RUDDER OFF caution was gone, and the right rudder was no longer X'd out. I looked down and saw both HYD needles steady at 3,000 PSI. To confirm that I actually had HYD 2A back online, I popped the speed brake out for a second--it worked. My mind was unable to process why my HYD 2A was working. Meanwhile, I thought about the international flights stacked above me.
I conferred with my wingman about trying a normal landing rollout to clear the runway for the heavies behind me. By now I had dumped down to 5,000 pounds of fuel, and my approach speed was 155 knots; the jet flew smooth and steady. I told him that I wanted to touch down and look for nosewheel steering (NWS) to come alive in the HUD as I assessed braking action, my line speeds, and the deployment of my speed brake. This would indicate that HYD 2A continued to work and I'd continue the rollout. Upon touchdown, if anything looked odd I would go to max-power, get the jet airborne and then take the arrested landing. My wingman concurred and confirmed that he was clear of the runway.
I went through my landing checklist one more time and confirmed my hook was up. Tower gave the winds and cleared me to land. I had about 10 knots in the face, which helped as well. As I touched down on runway 11, the NWS came alive in the HUD. The speed brake came out, and the braking action felt good. I had my line speeds made easily. I decelerated to a safe taxi speed and cleared the runway. My wingman was waiting for me, as I pulled off the active and contacted ground. We taxied to park, and I quickly prepared to shut down. But, before I shut down, he told me that the right aft fuselage of my aircraft was covered in hydraulic fluid and appeared to still be leaking. After shutting down, I jumped out and saw that both of the hydraulic fluid gauges were low. I took comfort that we got the jet on deck, and our trail maintenance det was scheduled to land in Darwin a few hours behind us.
What happened? A seal in the right rudder hydraulic servo had failed. Because the right rudder is powered by HYD 1B, this failing circuit began to deplete the HYD 1 reservoir. The RLS always shuts off the A-circuit first when trying to isolate a leak. This action obviously didn't fix the problem, so the hydraulic fluid continued to be pumped overboard. At 32 percent of capacity, the RLS shut down HYD 1B to isolate the leak. The right stabila tor/rudder-switching valve performed as advertised and began powering the same leaking servo with HYD 2A. As the leak continued the HYD 2 reservoir hit 60 percent, and RLS kicked in taking the HYD 2A circuit offline, leading to the combined HYD 1B/HYD 2A cautions.
Why did HYD 2A come back online after the emergency-gear extension? The arming valve is opened when the gear is emergency extended. This combines the charges of the APU accumulator and the emergency-brake accumulator to lower the gear. What I didn't mention earlier is that I had selected emergency brakes as part of my hook-skip game plan. This opens a valve, which effectively introduces these combined charges into the HYD 2A subsystem via the forward isolation valve. The HYD 2A subsystem essentially got enough of a boost to exceed the 1,500-psi threshold required to get it back online. The problem is that this didn't fix the leak, and the HYD 2A caution eventually would have returned as the fluid continued to purge.
What did I learn? This flight made me take a hard look at what I'll do with emergencies that lead you to the words "land as soon as practical." This is a great subject to broach in the ready room. Ask around and see what aircrew would do with various "land as soon as practical" scenarios. Some situations obviously are more varsity than others. The right answer with cycling HYD cautions is to get that airplane on the ground. In hindsight, the late decision to switch to a normal landing rollout game plan probably wasn't the right call. I was simply too worried about clobbering the airfield with my arrested landing. They've got gear there for a reason,. If you need it, use it.
A more conservative decision would have been to take the arrested landing. Although the HYD 2A stayed online long enough for me to land and park, it could have failed again, resulting in more problems and more chances of me punting this into the stands. Finally, I learned a lot more about the FA-18 hydraulic system. I've flown this aircraft for more than 10 years. But, I didn't fully understand how and why hydraulic leaks can transfer from HYD 1 to HYD 2 because of the configuration of the switching valves and servos.
As we continue to fly these glorious war machines well past their designed flight-hour limits, we'll continue to see components fail, perhaps sometimes in new and unexpected ways.
BY MAJ. BRIAN DENNIS, USMC
MAJ. DENNIS IS CURRENTLY AT COMMAND AND STAFF COLLEGE IN QUANTICO, VIRGINIA.
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|Date:||Sep 1, 2012|
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