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Standby for freestream.

The freestream recovery of a sonar dome is an emergency procedure (EP) commonly practiced in the MH-60R community. It is usually done in the simulator or without the dome actually in the water. That way you don't have to practice the emergency with a $2.8 million asset, hanging on a thin cable hundreds of feet below the aircraft. Our crew was flying in Lonewolf 710 and encountered this emergency.

Our squadron was onboard USS Nimitz (CVN 68), which was one month into its WestPac deployment. Lonewolf 710 had just gone through an A-phase maintenance inspection, and our maintainers had installed the airborne low frequency sonar (ALFS) sonar system. As the functional check pilot conducting the post-phase functional check flight (FCF), I wanted to make sure the ALFS would function should our squadron be tasked to conduct real-world, anti-submarine warfare (ASW).

The weather for the check flight was marginal, with scattered rain showers and patchy fog. However, we had the minimum visual-meteorological-conditions (VMC) of 1,000-foot ceilings and three miles of visibility to complete all our checks. We made our way through VMC as we cleared the carrier-control zone to find open airspace for the FCF. The ship drove on base-recovery course as she conducted fixed-wing flight operations.

Almost two hours into the flight, we had completed all required checks for the FCF and proceeded to op-check the ALFS. We had a newly installed dome, and the associated NATOPS procedure is to conduct an initial dip of 50 to 100 feet and then to fully seat the dome before conducting further dipping operations. We pulled into a hover at 70 feet and lowered the sonar dome to 90 feet water depth--a total of 160 feet of paid-out cable length (POCL). From the hover, we estimated the seas to be 5 to 7 feet.


After the initial op-check, we recovered the dome with no issues. We departed the hover and flew to the next dip location to conduct a full op-check at a greater depth. On the second dip, we lowered the transducer to 600 feet. We had another good op-check, so the crewman began to raise the dome with the reeling machine.

As the dome was about halfway up, we heard a loud squeal and smelled a strong metallic odor in the cabin. The reeling machine stopped with 307 feet of cable still deployed below the aircraft. Multiple error codes and cautions on the ALFS system were displayed. We were not even sure the transducer was still attached to the cable. Cable angle hover--the automatic-flight-control-system function that keeps the transducer cable centered underneath the aircraft --was disabled when the malfunction occurred and would not reengage.


For the next 20 minutes, the pilot at the controls (PAC) had to manually control the aircraft to maintain position over the oscillating cable. The rest of the crew worked to troubleshoot the emergency. The crewman tried to raise the dome using alternate methods, including auxiliary electric and auxiliary hydraulic modes, but the cable would not reel in.

At this point, the carrier was more than 20 miles away. As the pilot not at controls (PNAC), I started working bingo fuel calculations and communications. Since we were at an altitude of 70 feet, the ship was out of line-of-sight communications range. The squadron CO was airborne in Lonewolf 711, so our crew opted to use his aircraft to relay communications to the carrier about our situation. After 20 minutes of troubleshooting, we determined that we had no method to reel in the remaining cable. As a crew, we decided to execute the freestream recovery EP.

The freestream procedure involves climbing vertically at 100-to-350 feet per minute until the sonar transducer clears the water. Our crew decided to climb to 500 feet, which would give us nearly 200 feet of dome clearance from the water and at least 100 feet of clearance over the carrier flight deck. We slow-climbed to altitude and had the crewman visually verify that the dome was still attached to the cable once it cleared the water. With the dome trailing this far below the aircraft, NATOPs limits kept us to a maximum of 70 knots and 15-degrees angle of bank for the return transit.

We slowly started back to the ship and requested a minimum wind over the flight deck. We also asked for mattresses strapped to the deck on an open area to cushion the landing of the dome. Weather on the return transit deteriorated with ceilings dropping to 500 to 600 feet. The prevailing visibility dropped to one mile with intermittent rain, with winds increasing to 35 knots.

Onboard USS Nimitz, it was the most inopportune time to attempt the emergency recovery. The ship had just cancelled the majority of the fixed-wing cycle due to the weather, yet there was still a C-2 turning on cat 3 prepping to launch. The ship agreed to provide minimum winds over the deck for the recovery and slowed to four knots. Departure cleared the airspace around the CVN to make way for our emergency aircraft. The squadron XO made his way to the tower to assist with communicating with us. Squadron maintainers scrambled to locate and position the mattresses in front of spot 9.

After a slow transit, we made final preparations for landing. Because of the poor weather conditions, we had to orbit for about 15 minutes as the CVN made its way through a squall, disappearing from view at less than a mile on final.

We reviewed the procedures for shearing the cable in the event that we encountered further problems over or near the deck. We also discussed waveoff procedures if we slipped into the clouds or lost sight of the ship. The crewman positioned himself in the open cabin door, so he could spot the dome. With 307 feet of POCL, he lacked sufficient depth perception to judge the height of the dome over the deck. He was able to provide adequate calls regarding the dome's lateral and longitudinal position below the aircraft.

The PAC, in the left seat, flew a slow approach up the stern to spot 9 at 500 feet on the baralt. He skirted the bottom of the cloud deck and kept clearance between the hung dome and the flight deck. At that altitude, only the bow of the carrier was visible. All control inputs were based on calls from the crewman and nonflying pilot who could see just the tower below him. The PNAC provided conning inputs to keep the aircraft clear of the tower and antennae, while the crewman conned the dome into position over the mattresses.

The two single mattresses were side by side and looked no bigger than a postage stamp from 400 feet above the deck. However, with timely and accurate conning by the crewman and PNAC, and control inputs by the PAC, we managed to hit the target. We lowered the dome directly onto the mattresses.

Once the dome was grounded, maintenance crews rushed in and pulled the cable to the starboard side of the deck. We slowly descended and landed forward of spot 9, between the 1- and 2-wire.

Post-incident analysis of the aircraft revealed that the sonar cable fell out of the guides on the reeling machine, and the cable became pinched between the reel and the housing. This caused the reeling machine to seize during flight. The excess tension during the seizure caused the cable to break, leaving the dome attached to the aircraft only because the cable was being pinched in place. As a crew, we were fortunate that the $2.8 million dome assembly didn't depart the aircraft. The dome was inspected and reinstalled in a matter of days.


* Both the PAC and the PNAC were former MH-60R FRS instructors and had practiced manually controlling the aircraft with cable angle secured to keep the cable position centered. The task is not particularly difficult, but without sufficient experience, errant pilot inputs can induce excessive oscillations putting the dome and aircraft at risk. Just like learning to hover for the first time, it requires small inputs and patience to keep the dome stable.

* Cushioning the dome on a mattress or two sounds straightforward, but doing so from 400 feet requires solid conning commands from the nonflying crew and responsive inputs from the pilot. With a freestream conducted from higher altitudes, you might want to enlarge the area with more mattresses.

* CRM is not an abstract concept to which we simply give lip service. During the emergency and afterwards in the debrief, we commented how comfortable we were with the plan that evolved during the procedure, including bingo, wave-off criteria, communications and contingencies. Each member was clear on their tasks and we effectively backed-up each other throughout.

Our success started well before the flight by briefing clear expectations of crew responsibilities during emergencies, and then sticking to those expectations during the flight.


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Author:Eckhoff, Justin
Date:May 1, 2014
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