An aircraft carrier is a pretty amazing thing. Essentially, it can launch planes from anywhere. But even though aircraft carriers are huge, they aren’t big enough for planes to take off or land in a normal method. The USS Dwight D. Eisenhower (CVN 69) has about 500′ for landing planes. In order for planes to be able to successfully land in that distance, it is equipped with an arresting wire system, which can stop a 54,000 lb. aircraft travelling 150 miles per hour in only two seconds and a 315′ landing area. This system consists of 4 arresting cables, which are made of wire rope coiled around hemp. These ropes are very thick and heavy and cause a significant risk to personnel safety if they are parted or detached.
This is what happened on March 18, 2016 while attempting to land an E-2C Hawkeye. An arresting cable came unhooked from the port side of the ship and struck a group of sailors on deck. At least 8 were injured, several of whom had to be airlifted off the ship for treatment. We will examine the details of this incident within a Cause Map, a visual form of root cause analysis.
The first step in any problem investigation is to define the problem. We capture the what, when, and where within a problem outline. Additionally, we capture the impacts to the goals. The injuries as well as the potential for death or even more serious injuries are impacts to the safety goal. Flight operations were shut down for two days, impacting both the mission and production/ schedule goal. The potential of the loss of or (serious damage to) the plane is an impact to the property goal. (In a testament to the skill of Navy pilots, the plane returned to Naval Station Norfolk without any crew injuries to the flight crew or significant damage to the plane.) The response and investigation are an impact to the labor goal. It’s also useful to capture the frequency of these types of incidents. The Virginian-Pilot reports that there have been three arresting-gear related deaths and 12 major injuries since 1980.
The next step in the problem-solving process is to determine the cause-and-effect relationships that led to the impacted goals. Beginning with the safety goal, the injuries to the sailors resulted from being struck by an arresting cable. When a workplace injury results, it’s also important to capture the personal protective equipment (PPE) that may have impacted the magnitude of the injuries. In this case, all affected sailors were wearing appropriate PPE, including heavy-duty helmets, eye and ear protection. This is a cause of the injuries because had they NOT been wearing PPE, the injuries would have certainly been much more severe, or resulted in death.
The arresting cable struck the sailors because it came unhooked from the port side of the ship. The causes for the detachment of the cable have not been conclusively determined; however, a material failure results from a force on the material that is greater than the strength of the material. In this case the force on the arresting cable is from the landing plane. In this case, the pilot reported the plane “hit the cable all at once”, which could have provided more force than is typical. The strength of the cable and connection may have been impacted by age or use. However, arresting cables are designed to “catch” and slow planes at full power and are only used for a specific number of landings before being replaced.
Other impacted goals can be added to the Cause Map where appropriate (additional relationships may result). In this case, the potential damage to the plane resulted from the landing failure, which was caused by the detachment of the arresting cable AND because the arresting cable is needed to safely land a plane on an aircraft carrier.
The last step of the Cause Mapping process is to determine solutions to reduce the risk of the incident recurring. More investigation is needed to ensure that the cable and connection were correctly installed and maintained. If it is determined that there were issues with the connection and cable, the processes that lead to the errors will be improved. However, it is determined that the cable and connection met design criteria and the detachment resulted from the plane landing at an unusual angle, there may be no changes as a result of this investigation.
It seems unusual that an investigation that resulted in 8 injuries would result in no action items. However, solutions are based on achieving an appropriate level of risk. The acceptable level of risk in the military is necessarily higher than it is in most civilian workplaces in order to achieve desired missions. Returning to the frequency from the outline, these types of incidents are extremely rare. The US Navy currently has ten operational aircraft carrier (and an eleventh is on the way). These carriers launch thousands of planes each year yet over the last 36 years, there have been only 3 deaths and twelve major injuries associated with landing gear failures, performing a dangerous task in a dangerous environment. Additionally, in this case, PPE was successful in ensuring that all sailors survived and limiting injury to them.
To view the outline and Cause Map of this event, click on “Download PDF” above.