While helicopters are not new to naval service, the overall health of helicopter naval aircrewmen has worsened in the past two decades. The helicopter will remain a cornerstone of the fleet, however. In 2012, Sikorsky Aircraft signed a contract with the U.S. military for roughly $11 billion to ensure the Navy will continue to receive support for its fleet of MH-60 helicopters, which are responsible for a myriad of missions, including strike coordination, reconnaissance, antisubmarine warfare, mine warfare, and search and rescue.
In the era of the MH-60, there has been a much higher rate of aircrewmen reporting back and neck pain.1 Evidence suggests a strong correlation between this increasing problem and the effect of long-duration exposure to the whole-body vibrations helicopter aircrew routinely experience. Fortunately, there is enough research on helicopter back pain to make meaningful changes in the short term, allowing the Navy to provide a safer and healthier work environment for this community right away. The Navy recently took an important step in this direction when it began installing more ergonomically friendly gunner seats in the MH-60S Seahawk. But much more needs to be done.
Clinically, back pain falls into three categories. Acute back pain impacts performance for less than four weeks; subacute back pain between four weeks and three months; and chronic back pain beyond three months.2 Acute in this context has nothing to do with the amount of pain felt. Aircrew often feel intense pain—a burning sensation down the spine and into the leg, for example—for months when performing routine duties. Nevertheless, when faced with the prospect of being medically sidelined from flight duty, many understate or decline to report the problem until it becomes unbearable.
A high prevalence of back pain among naval helicopter aircrewmen was identified many years ago. In 1996, the Naval Health Research Center published a study on pilots and aircrewmen. It found back pain experienced by aircrew was more than three times the amount experienced by pilots, increasing dramatically with age.3 Of all the vibrational frequencies researched, the human body is the least tolerant of those a helicopter produces, specifically vertical axis vibrations.4 Over time, microtraumas develop in the spine.
Whole-body vibrations (WBVs) are the reason behind microtraumas. They also are known to cause thoracic fractures and herniated disks.5 A 1990 study of 163 helicopter pilots suggested that more serious subacute back pain develops when the length of the vibration dose is increased.6 The same study also noted a rise of diagnosed chronic back pain the more flight time is accumulated over an aviator’s career. Several other studies investigated possible causal factors for rotary-wing (RW) back pain. Height, weight, tobacco use, physical fitness level, and total flight time were found to have little association with subacute back pain in the RW community.7 However, there was a noted predictive factor for chronic back pain. Once subacute back pain is experienced, there is an increased likelihood of the situation repeating itself. And the more subacute back pain experienced, the more likely it is a sailor will develop chronic back pain.
Chronic back pain leads to fewer aircrew available to fly, and it costs the government more money in retirement disability claims. The issue is also felt immediately at the deckplate level. The aircrew community has been undermanned for more than a decade and the problem is exacerbated by this medical issue. While aircrewmen are more likely to delay reporting initial back pain to remain in a flying status, once they reach the chronic pain level, aircrew leave the service as they realize the benefits do not outweigh the cost.
Impact of Lengthier Flights
The Navy is currently addressing workspace ergonomics by making stand-up desks more widely available, recognizing the issues associated with being in a cramped seated position for prolonged periods. But stand-up desks do little to help helicopter aircrewmen. The helicopter is even more cramped than most shipboard working spaces and includes unnatural vibrations. Some research suggests aircrewmen experiencing WBVs for an extended period in a position that contorts the spinal column more than sitting at a desk likely will experience even greater long-term damage.
In reviewing aviator flight logbooks over the past several years, a colleague and I determined that the number of four- and five-hour flights has increased significantly, even though total flight hours are decreasing because of monthly flight-hour limits and maintenance issues. If the 1990 study is correct, this longer continuous exposure to WBVs will result in greater stress on the disks in the lower spine, leading to more fractures and herniated disks. The longer the body feels the stress in a single dose, the faster the fracture develops. If the vibrations are interrupted (for any reason), the stress also is interrupted, giving the body time to heal. Thus, limiting training flights to no more than three hours should reduce the length of time WBVs have to inflict damage on the spine. Not only will this improve aircrew health and availability, it also could increase retention rates.
Lighter Flight Equipment Needed
An investigation into flight equipment found that 69 percent of aviators reported an increase in back pain when any weight was added to their flight equipment.8 Adding extra weight and bulk to a human frame adds more strain on the lower back and neck. At 30 lbs, the CMU-37/38 aircrew endurance vest is beginning to replace the heavier CMU-33. This is an improvement, but there is an even better vest in service. The PRU-70 was designed by naval aviation’s Aircrew Systems program office (PMA-202) in 2008 and sent to the fleet the following year.
The PRU-70 weighs only 20 lbs—slim compared with other flight vests. It fits better, is smaller, and allows aircrewmen to move freely in and out of the aircraft. However, the current guidance is to issue only the CMU-37/38 and recall all PRU-70s. This is a mistake. The PRU-70 should be the primary vest. It weighs 10 lbs less, is already in the system, and still carries the body armor required for all missions.
The Navy also should approve the OPS-Core® helmet for aircrewmen, as it has already been tested by a fleet replacement squadron and a search-and-rescue command performing high-risk missions in mountainous terrain. These helmets are more comfortable, could save the Navy from $710,000 to $1,730,000 based on my calculations, and are built to reduce neck and back issues that result from extensive use of night-vision devices.
These are simple changes that can reduce the impact of WBVs to improve aircrew neck and back health and, by extension, Navy helicopter community readiness—and hopefully retention. Doing anything less would fail to keep faith with sailors.
1. Rob Perry, “NAVAIR Delivers MH-60S Gunner Seat Replacement to the Fleet,” Naval Aviation News, 25 November 2019, navalaviationnews.navylive.dodlive.mil/2019/11/25/navair-delivers-mh-60s-gunner-seat-replacement-to-the-fleet/.
2. Amir Qaseem, Timothy J. Wilt, Robert M. McLean, and Mary Ann Forciea, “Noninvasive Treatments for Acute, Subacute, and Chronic Low Back Pain: A Clinical Practice Guideline from the American College of Physicians,” Annals of Internal Medicine, 4 April 2017, annals.org/aim/fullarticle/2603228/noninvasive-treatments-acute-subacute-chronic-low-back-pain-clinical-practice.
3. C. M. Simon-Arndt, H. Yuan, and L. L. Hourani, “Aircraft Type and Diagnosed Back Disorders in U.S. Navy Pilots,” Naval Health Research Center, 26 December 1996, apps.dtic.mil/dtic/tr/fulltext/u2/a319230.pdf.
4. R. P. Delahaye, R. Auffret, P. J. Metges, J. L. Poirier, B. Vetes, and H. Viellefond, Physiopathology and Pathology of Spinal Injuries in Aerospace Medicine (2nd Ed.), NATO Advisory Group for Aerospace Research and Development, AGARD-AG-250, (English) 1982, 48–53, 226–60, 276–80, 293–96.
5. Delahaye et al., 293–96.
6. P. M. Bongers, C. T. J. Hulshof, L. Dykstra, and H. C. Boshuizen, “Back Pain and Exposure to Whole Body Vibration in Helicopter Pilots,” Ergonomics 33 (1990): 1007–26.
7. For example, see: R. S. Bridger, M. R. Groom,
H. Jones, R. J. Pethybridge, and N. Pullinger, “Task and Postural Factors Are Related to Back Pain in Helicopter Pilots,” Aviation Space Environmental Medicine 73 (2002): 805–11.
8. R . L. Nevin and G. E. Means, “Pain and Discomfort in Deployed Helicopter Aviators Wearing Body Armor,” Aviation Space Environmental Medicine 80 (2009): 807–10.
