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Off the coast of Japan in November 2023 three CV22 Ospreys were preparing for what should have been a routine training mission. After a refueling and maintenance stop in Iwakuni, two of the three Ospreys took off to practice refueling with a C130 and perform a free fall water jump, with the third Osprey trailing one hour behind in support. The two leading Ospreys, Gundam 21 and 22, carried 23 crew members, 15 in Gundam 21 and 8 in Gundam 22. 40 minutes into their flight Gundam 21 received a message from its sister aircraft.
"We have three chip burn advisories, but plan on continuing the mission. "Copied" 10 minutes later, Gundam 21 saw Gundam 22 start to head east, deviating from their planned south bound route. Right after Gundam 21 received another message "We got chips" "Do you need support" "Negative, continue mission" Gundam 22 was now heading east toward Yakushima, a landing site just 15 minutes away, despite the availability of closer alternatives. As they approached, they initiated communication with tower control. "This is Gundam 22, we are requesting to land on runway 3 2" "There is traffic on the runway, is this an emergency?" "Affirmative" This was the first and only mention of an emergency given by the crew.
Waiting for the runway to clear out, the CV22 osprey did one last right turn loop before performing its landing approach at 300 meters over sea level. Just two minutes prior to landing the left nacelle caught on fire, 6 seconds later the osprey went through a hard roll, it fell from the sky and impacted the water. What followed was the immediate grounding of all Japanese and American Ospreys. A search and rescue operation began right away and lasted for 48 days. While some remains washed ashore, the main hull and its eight
crew members were found a month later by divers, 30 meters deep near the crash site. The Osprey is an impressive machine, a hybrid of helicopter and airplane. In theory, it overcomes many of the limitations of helicopters by flying at speeds over 200 knots and covering greater distances, all without needing the long runways required by conventional planes. But, this latest crash only adds to the list of fatal accidents involving the aircraft. So let's take this opportunity to look deeper into the V22 Osprey. Is it safe? How does it work? And how did they figure out what happened to the osprey that crashed in Japan.
The inception of the Osprey came out of necessity. In 1980, in the midst of the Iranian Revolution, a cascading sequence of events led to a hostage crisis where a group of Iranian militants stormed the US embassy in Tehran and took 54 hostages. To extract the hostages the US needed to use heavy lift helicopters. The RH 53 Sea stallion offered a way to approach the embassy from above to make extraction easier. But Tehran was too far outside the range of the Sea Stallions that were stationed aboard the USS Nimitz 96 kilometers outside the coast of Iran. Sea Stallions, like all helicopters, have a limited range since hovering consumes fuel needed for forward flight. They also face speed limits.
As they travel forward, one side of the rotor moves forward while the other retreats backwards. Meaning, with the relative velocity of the helicopter added, one side of the rotor is travelling faster than the other. Eventually the helicopter can't travel faster as shock waves and flow separation will occur on the advancing blade tips. Despite being one of the fastest helicopters, with a top speed of 360 kilometers per hour and a range of 1,000 kilometers, The Sea Stallion still couldn't cover the nearly 1,400 kilometers between the Nimitz and Tehran. The plan therefore included a refueling stop for 8 helicopters in the middle of the desert using 3 C130 cargo planes. The location was named desert one.
However this plan quickly descended into chaos. As the first C-130 landed, a bus filled with 43 Iranian civilians was seen approaching. The personnel stopped the bus and as they were unloading it, a fuel truck was seen approaching from the other side and it wasn't slowing down. With the mission at stake, the soldiers shot at the fuel truck which erupted into a giant fireball. Illuminating the mission location for all to see. Further south, the squadron of 8 Sea Stallions, codenamed BlueBird 1 through 8, were already facing challenges as a sandstorm had formed between them and Desert One.
A warning light flashed in the cockpit of Bluebird Six. Something was wrong with one of its blades. The blade rotors were hollow and filled with pressurized nitrogen. This pressure was monitored to detect cracks in the rotor blades. When Blue Bird six's light went off it signaled that the rotor was compromised and they needed to land immediately. The crew of Bluebird Six abandoned the helicopter in the desert and transferred to another helicopter that had landed to assist. The mission was now down to seven helicopters.
The remaining choppers pressed on through choking dust clouds, which cut visibility to meters. Bluebird Five faced electrical failures leaving the pilot with barely functioning flight instruments. Flying basically blind and unable to locate the other helicopters or assess weather conditions at Desert One, the crew of Bluebird five decided to turn back, unaware they were just 25 minutes away from clear skies. The mission was left with the bare minimum of six helicopters needed to continue. As the six helicopters approached Desert One, they saw the giant fireball illuminating their landing spot.
The plan from here was to refuel and regroup 92 kilometers east of Tehran at Desert Two. The sand and the heat had caused too much damage to one of the helicopters causing its hydraulic system to fail pushing the number of functioning helicopters below the planned mission's abort threshold. Amid the chaos with civilians nearby and a massive fire raging at the heart of a covert mission the commanding officer made the difficult decision to abort the mission and retreat. This mission failure highlighted the need for a new heavy lift aircraft that could have made the 1400 kilometer trip and was also capable of hovering for extractions.
Enter Bell Helicopters, which had been experimenting with hybrid aircraft since the 1950s. At the time, there wasn't much interest in a craft that was less efficient than a helicopter at hovering and less capable than an airplane in flight. But with NASA's support, Bell developed a vertical takeoff and landing demonstrator, resulting in the successful testing of the XV-15 by the 1970s. When Operation Eagle claw failed, the Marine corps decided to give Bell the go ahead to develop the XV15 technology further into the V22 Osprey. The next two decades saw the concept refined from a test bed to a functioning aircraft, with first hover in March of 1988 and a first fixed wing flight two months later. Since then, Bell and Boeing have provided
three Osprey variants to the U.S. military: the MV-22 for Marine transport and rescue, the CV-22 for Air Force special operations, and the CMV-22B for Navy replenishment. The core feature of the V-22 Osprey is its unique tiltrotor system. In helicopter mode, the pilot uses helicopter controls that use a fly by wire system to control the actual maneuvering mechanism. The collective pitch of the proprotor blades enables the aircraft to hover, while roll is controlled by changing the collective pitch of the blades in opposite directions. Pitch is achieved by tilting both rotors in the same direction,
and yaw is controlled by tilting the rotors in opposite directions. This precise control allows the V-22 to hover, take off, and land vertically with ease. When transitioning to airplane mode, the V-22 tilts its rotors forward until they function as traditional propellers, providing thrust for forward flight. In this mode, the aircraft's control surfaces, including the ailerons, rudders, and elevators, take over the primary control functions. [SLIDE 5] The transition between helicopter and airplane modes is controlled by a small knob on the pilot's controls.
Pilots are trained to use only a few specific tiltrotor angles to avoid complex aerodynamics. With just their thumbs, the crew can adjust this dial, which sends a signal to the fly-by-wire system. In helicopter mode, the nacelles tilt between 80° and 97.5°, usually staying at 90°. Mechanical stops at 0° and 97.5° ensure the nacelles don't go beyond these limits. The pilots can make short landings with the nacelles tilted between 90° and 60°. The actual tilting mechanism, located at the edge of the wing, uses a hydraulic motor to turn a long telescoping screw. One end of the screw is attached to the wing, and the other to the tilting nacelle; as the screw extends, the nacelle tilts upwards.
The V-22's nacelles rotate independently, so precise control systems are crucial. Any small difference in the nacelles position during hovering could cause a catastrophic crash. The proprotors serve a dual purpose, generating lift in helicopter mode and providing thrust in airplane mode. This blend of airplane propeller and helicopter rotor functions is what gives them their unique name, proprotors. Their dual function is clear by simply looking at them. The C130 has propellers that are 4 meters in diameter. At the other extreme the Sea stallions rotor has a diameter of 21 meters. The V22 proprotor sits in the middle with 11.6 meter proprotors.
Another aerodynamic trade-off with the V-22 is in the twist of its proprotor blades. Helicopter blades usually have an 8-degree twist. But the V-22's proprotors also need to act as efficient propellers when the incoming airspeed is much faster. To handle this, the proprotors have a 47-degree twist. While this improves efficiency in forward flight, it comes at the cost of reduced hover efficiency. [REF] Hover efficiency is measured by disk loading, the ratio of an aircraft's weight to the rotor's circular area. A rotor works by pushing air downward to generate upward lift. For Helipoters
it's easier to create this lift by moving a larger volume of air slowly rather than a smaller volume quickly. The V-22 is heavy and has a small rotor, resulting in an inefficient hover with a high disk loading. This high disk loading means that to hover, the Osprey needs to push down more air at faster speeds than a helicopter. For a helicopter this downwash is normally around 60 knots, hurricane winds are around 64 knots and the V22 has a downwash of 80 knots. Which can make ground crew operations a little difficult. The V-22 Osprey's tilting nacelles and intricate mechanics rely on a network of five gearboxes and a complex shaft system to function,
which comes at a high risk. Every component is an extra point of failure. So, how does this system work, and what exactly went wrong during the training flight in Japan? The propeller gearboxes of the Osprey are nearly identical, with a key difference in the right gearbox, which has one less gear to enable the proprotors to rotate in opposite directions. The aircraft is powered by two Rolls-Royce turbines and an auxiliary power unit that assists in rotating the entire wing assembly parallel to the fuselage, a necessary feature for storage on an aircraft carrier. In helicopter mode, even a slight difference
in the rotation of the V-22's proprotors could create significant asymmetrical forces, leading to instability and large roll movements. To prevent this, the proprotors are linked by a shaft, like in other dual-rotor helicopters. But unlike traditional designs, the V-22's rotors are not linked by a straight line, they are connected through its wings. From above, you'll notice the V-22's wings are swept forward. While this isn't typical for planes, it's not about aerodynamics. The forward sweep gives the large proprotos enough clearance to avoid colliding with the wings. A straight wing would require the heavy, tilting nacelles to be pushed farther out, creating more structural and aerodynamic challenges.
Viewed head-on, you'll see the wings tilt upward slightly, by just 3.5 degrees. This subtle dihedral angle not only adds stability during airplane mode but also ensures that when the wings are folded parallel to the fuselage for storage, the nacelles have enough clearance to rotate smoothly into position. So instead of one continuous straight shaft, The V-22's shaft is split into six sections to handle the 13-degree wing angle and share power between the engines, allowing the V22 to be powered by a single engine if necessary.[REF] But the nacelles are not rigidly fixed to the wing, so an extra gearbox is needed.
The tilt-axis gearbox transfers power from the interconnected shaft to the proprotor gearbox no matter the angle the nacelle is positioned. The gearboxes need oil to keep everything running smoothly, reducing friction and keeping the gears meshing properly. The oil also doubles as a way to monitor the health of the gearbox. As gears wear down, they shed tiny harmless particles called "fuzz," especially during break-in. The real problem comes when failing gears produce bigger metal chips. How can the system detect and remove these chips without opening the gearbox and replacing the oil?
A small magnetic detector can be placed in the oil flow to attract the metallic chips. It has two open contacts that close when a metallic chip touches them, acting like a switch. A pulse of electricity is then sent through the chip to melt it. Bigger chips need more energy and pulses, and if a chip is too large to burn off, the system alerts the pilots. This chip detector is the one that was mentioned in the latest Osprey crash. Each proprotor gearbox has three separate chip detectors that all work together to collect and burn chips. From the conversations with the tower and the other Osprey,
the investigators knew that there was a problem with the chips, even before recovering the aircraft. They just didn't know what part had failed. Once recovered from the ocean floor, the flight log filled in the gaps of information left by the conversion with the tower and the sister osprey. In the span of half an hour the system reported that it had successfully burned 5 chips. Protocols say that one alarm is merely a warning, but once three chip burns occur the crew should "Land when practical".
However, landing is ultimately at the pilot's discretion, as other factors may affect the urgency of the alarms. In this case, the crew believed the alarms were caused by a faulty chip detector. Three minutes after the fifth chip burn, the system issued a warning that a chip could not be burned. Protocol at this stage requires the crew to land as soon as possible if no secondary effects are observed, or to perform an immediate landing or controlled ditching if there are signs of overheating. This is when the crew decided to divert. For unknown reasons, the crew chose to land at an airfield 15 minutes away, despite closer and suitable options being available. Voice recordings revealed no sense of urgency,
and once the pilot made the decision, there was no further discussion about the choice. Sadly, as the Osprey came into the final approach, the left nacelle caught fire causing a catastrophic failure of the propulsion system. From that point forward, the crew could not have done anything to save the aircraft. After the aircraft was recovered, tests on the left nacelle found no fuel or hydraulic contamination. The three chip detectors were removed and they were all surrounded with debris. After they were cleaned the investigators confirmed that they were functioning properly. The gearbox failure was evident from a broken gear in the proprotor gearbox,
with the drive train showing severe wear and gear teeth ground nearly smooth. [SLIDE 11] After a crash off Japan, the Osprey fleet was grounded for months. Limited flights resumed in March, but the aircraft still isn't performing its full range of missions, including carrier operations. This crash was the fourth since 2022, with incidents involving previously unseen mechanical failures. For example, In June 2022, a clutch failure caused a crash that killed five Marines. The clutch had worn out faster than expected. In that incident, a rare dual clutch engagement left the pilots unable to save the aircraft.
This string of crashes has reignited questions about the safety and reliability of the V-22 program. Since its inception the V22 has been seen as an unsafe vehicle even earning it the nickname "widow maker". But what does the data say? Like any groundbreaking technology, the introduction of the world's first tiltrotor aircraft involved a steep learning curve. The large capacity of the V22 means that these accidents carry a larger risk with the added personnel on board. In 2000, during a training exercise one V22 osprey descended too fast in helicopter mode and crashed, killing the killed 19 crew members. When any helicopter descends too quickly, air starts flowing upward near the hub
area where the blades are traveling slower, causing the center section to stall. As this happens vortices form near the center of the rotor, that then causes a sudden loss of lift While no mechanical failure was the culprit of the accident, after the investigation the V22 were limited to descending at a maximum of 4 meters per second. [REF] Just a couple of months later, a faulty hydraulic line caused another crash adding four more deaths. These two back to back accidents severely tarnished the program's reputation, and has led to a lasting negative public perception. But what does the data say?
Since 1991, there have been 25 incidents involving the V-22, nine were caused by pilot error, ten by mechanical failures, two were a mix of both, and two are still under investigation. [REF] This has led to the unfortunate death of 58 service members and has injured another 52. But how does this compare to two other helicopters, the Sirowsky H60 and the Chinook H47? Since its debut in 1979, the H-60 and its variants have had 390 incidents, resulting in 970 deaths. Sixty of those deaths happened in the last decade, which is two more than the V-22 has caused over the past 30 years.
The H-47 has historically had the Army's highest death rate per incident. Between 1966 and 2005, 238 lives were lost in 10 non-combat crashes. But in recent years the H47 Chinook has had a huge improvement in safety with 47 incidents and no deaths between 2016 and 2020. Simply comparing the number of deaths does not take into account how many aircraft have been built and how much they fly. In accidents per airframe the V22 fairs quite well with only.0625 incidents per aircraft, compared to.075 and.11 for the H60 and the H47. But if you look by how much flight time, the V22 has more deaths per 100K hours
This data shows a couple of trends. Larger aircraft, like the V-22 or H-47, tend to have higher death rates per incident because they carry more people, increasing the risk per crash compared to smaller aircraft like the H-60. Also, more complex aircraft usually see a spike in incidents early on as problems are identified and fixed, but these issues tend to decrease over time as the aircraft matures and systems are improved. These comparisons are not intended to put the V-22 above other military aircraft or dismiss its safety record. No aircraft is without flaws, and every accident is a stark reminder of the risks faced by service members. However,
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