Medical Helicopter Blades Break Apart After Takeoff
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On the morning of August 31, 2008 a medical helicopter crashed shortly after take-off from a local fundraising event just outside of Greensburg, IN. On board were the pilot, Roger Warren, 43, flight paramedic, Wade Weston, 38, and flight nurse Sandra Pearson, 38. All three died in the accident.
This helicopter was owned and operated by Air Evac Lifeteam, originally based out of West Plains, MO. Air Evac is one of the largest air medical providers in the United States with over 140 helicopters across 15 states and are a part of the one of the largest air medical provider groups in the world, Global Medical Response.
The aircraft itself was manufactured by Bell Helicopters and was a model 206 Long Ranger, which is one of the most highly produced helicopters in the world and also one of the safest. This particular aircraft was built in 1979 and had a Rolls-Royce/Allison model 250c30p turboshaft engine. This aircraft had 26,250 hours on the frame with 11,554 hours on the engine itself. It was last inspected by the FAA just 10 days before this accident on august 21, 2008. The blades for this helicopter had 2,808 hours on them and still had almost 800 hours left in their service life. The accident pilot was a 43-year-old male who held a commercial pilot certificate with ratings for both rotorcraft helicopter and single-engine airplane. His certificate also included instrument ratings for both helicopters and airplanes. The pilot had worked for AirEvac for just over 2 years with his last check ride taking place just 2 months prior to the accident on June 10th. He had a total of 5,493 hours of total flight time with 5,176 of them in helicopters with 1,915 hours on this type.
About a week before the accident a maintenance discrepancy was documented that stated, "While on approach heard (and) felt low rumble (and) vibration from rear of aircraft." The resulting maintenance inspection did not reveal any anomalies. A ground run and flight check could not duplicate the write-up, nor did they identify any other discrepancies. There was no mention of a similar discrepancy in the maintenance records subsequent to that event.
The accident helicopter was based out of Rushville, Indiana, which was located about 18 miles north of the accident site. It was lunch time, and the weather was clear and warm with 10 knot winds.
The crew was doing a local PR/fundraising event at a local fire station that day. In the United States, especially across the midwest part of the country, ground providers often times have a choice as to what medical helicopter company they want to show up and transport their patient. So it is not uncommon for the flight crew, which usually consists of a single pilot, flight paramedic, and flight nurse, to fly out and visit with the local EMS, fire, and police agencies in their coverage area. They may provide outreach education, gives tours of the helicopter, provide landing zone safety classes, or simply hang out with the ground providers all in an effort to build relationships and do some networking. In this case, the PR event was a picnic at the Burney Volunteer Fire Department.
The crew arrived at this fundraising event at 11:50 AM and were all done by about 1:00 PM. They lifted off the ground at the PR event 1:17 and just a few moments later witnesses on the ground stated that they began to see parts fly off the helicopter when it suddenly began a rapid descent and crashed just a few minutes after take-off.
The helicopter crashed into a cornfield just 1.2 miles from the PR event. The fuselage came to rest nearly inverted, and the entire cockpit and cabin areas were destroyed by impact forces and a post-impact fire. The crash occurred with such force that the transmission became separated from the airframe and came to rest almost 200 yards northeast of the main wreckage.
At the accident site, investigators could quickly see that the main rotor blades were still attached to the hub. One of these blades was still fully intact, but the other blade was fractured into 3 separate pieces with the most inboard piece still attached to the hub. Both of the other sections of the blade were recovered from the accident site.
Burney Fire Department, which was the very place where the flight crew was just holding their PR event, responded to the accident and were on scene within 2 minutes. All of the wreckage was recovered and transported to a hangar for investigation and analysis by the National Transportation Safety Board (NTSB), Air Evac, and Bell helicopters. Based on the eyewitness testimony of parts flying off of the aircraft and that one of the rotor blades was separated into 3 sections, the investigators quickly began to focus their efforts on the main rotor blades.
The rotor blades on the Bell 206 are a bonded assembly where there are several layers and skins, wrapped around an aluminum honeycomb core, and all bonded together with high strength adhesives. A full metallurgical examination was conducted on the fractured blade. There was a very clean and complete fracture that was found about 8 feet from the tip of the blade with another, very irregular fracture, found about another 3 and half feet inward from the first fracture.
Further examination of the blade revealed ratchet marks as well as fine elliptical clamshell marks, both of which are consistent fatigue cracking. Now, even without the use of a microscope, clamshell marks were visible and the crack clearly emanated from inside the blade between the leading edge and the upper wall. The crack propagated upwards and actually encompassed about 50% of the cross section of the blade before the entire blade failed and fractured. Utilizing a scanning electron microscope, investigators were able to narrow it down and isolate a single pore on the inner surface of the blade spar. The crack that ultimately fractured this blade and caused 3 fatalities actually emanated from this tiny single spot on the blade.
On the outside of the blade there was no evidence of corrosion or any previous mechanical damage, so it was pretty easy to rule out that some external force had caused this failure. The outer wall of the blade is made of aluminum but to add mass to the rotating structure, lead weights are added to the inside of the blade spar, and they run the length of the blade. This lead weight is held in place by adhesive placed in between the weight and the main spar of the blade. When investigators located the origin of the previously mentioned fatigue crack, they also noticed that there was a large void, or empty space, in the adhesive between the inside surface of the spar and the lead weight. This void was over 9 inches in length and extended in both directions from the original crack.
Bell noted that excessive voids between the main spar and the lead weight can lead to a fatigue failure in these blades, such as what occurred in this incident. In short, this blade failed because there was a void in this adhesive during the manufacturing process and this void allowed too much stress to be placed upon the blade during normal operation which ultimately led to a crack forming which eventually made its way all the way through the blade, fracturing the blade completely, which finally led to the aircraft crashing.
As a result of the investigation, and almost a full year later, Bell helicopters did release an Alert Service Bulletin in July of 2009, which included all of the affected airframe models as well as all of the blades affected by serial number. This was a major service bulletin and a huge undertaking that affected aircraft from all over the world. If the conditions were met by the bulletin, all affected blades had to be removed and actually x-rayed in the affected area. All radiographs would then be sent back to Bell helicopters for review. If the blade was found to have a crack, then Bell would replace the affected blade. If the blade did not have a crack, then the blade would have to be physically checked by hand with a recurring blade spar wipe check for a crack every 60 engine starts for the remainder of the life of the blade.
Upon completion of the investigation, the NTSB found that the probable cause for this accident was “The in-flight separation of a main rotor blade due to a fatigue failure of the blade spar, rendering the helicopter uncontrollable, and the manufacturer's production of main rotor blades with latent manufacturing defects, which precipitated the fatigue failure of the blade spar.”
This is one of the very few cases involving EMS helicopter crashes, where everyone involved with operating this helicopter did everything right. They checked the aircraft as they were supposed to. They followed all the rules and adhered to all of the manufacturer and operator guidelines. But, due to a manufacturing defect, these 3 people tragically lost their lives.
Full video investigation can be found here:
A lawsuit was later filed by the estate of the flight nurse killed in this accident. Without acknowledging any wrongdoing, Bell Helicopters settled the lawsuit for $5.6 million.
While the cause of this accident was clearly a defect in Bell’s manufacturing process, Bell can be commended for cooperating and participating in the lengthy investigation and releasing a service bulletin that clearly acknowledges the manufacturing issues so that they could quickly identify and replace any other defective parts in order to prevent further accidents and further loss of life.