Public Service, Regulatory

NTSB: Weight Errors, Improper Oversight Led to Crash

By By Andrew Parker, Managing Editor | January 1, 2011
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While acknowledging the role of lax oversight by maintenance inspectors, FAA and the U.S. Forest Service, the National Transportation Board has placed much of the blame for a 2008 crash of a Sikorsky S-61 on the operator—Carson Helicopters. During a public meeting Dec. 7 coinciding with the release of the accident’s probable causes, board members touched on the many complicated aspects of the two-year investigation, which involved 23 NTSB staff members, more than five percent of the organization’s total workforce of around 400 people.

Shown here is the accident helicopter prior to the August 2008 flight. Courtesy NTSB

The S-61 went down shortly after taking off on Aug. 5, 2008 in the mountains near Weaverville, Calif. Nine people died in the crash, including the pilot and seven Oregon firefighters, and four others on board were seriously injured. Carson was operating the helicopter under a U.S. Forest Service contract.


NTSB concluded that the main causes of the crash were Carson’s “intentional” understatement of the helicopter’s empty weight; altering of the power available chart (to exaggerate lift capability); and practice of using above minimum specification torque figures in performance calculations, which resulted in the pilots overestimating the load capability of the S-61. Also cited was “insufficient oversight” from FAA and the Forest Service. Contributing factors included the flight crew’s failure to recognize the performance discrepancies during two departures prior to the accident flight.

Accompanying the probable causes are a series of 11 recommendations to FAA and 10 to the Forest Service. See the full list at and the accident docket at

After an overview from investigator-in-charge Jim Scheuster, board members heard presentations covering helicopter performance, operations, the role of oversight, seats/restraints and fuel filtering.

At the center of the investigation are a series of “altered” performance charts and records that show the pilots were using incorrect calculations for weight, resulting in a payload that closer resembled emergency takeoff procedures. NTSB staff explained that the accident helicopter’s actual weight was 13,845 lbs, but a Carson-supplied chart identified it as 12,408 lbs—a difference of 1,437 lbs. This difference led the pilot to miscalculate the hover out of ground effect (HOGE) limitations of the helicopter. Using the correct weight number, the maximum HOGE weight of the S-61 was 18,445 lbs, and the allowable weight was 15,840 lbs. Due to the altered charts, the helicopter took off at a total weight of 19,008 lbs—more than 500 lbs over the maximum HOGE weight. Essentially, the S-61 was operating in emergency takeoff conditions.

Board member Robert Sumwalt felt that the “most appalling” aspects of the accident are Carson’s intentional understatement of the operational figures and falsification of maintenance documents, and “the lack of government oversight to this problem.”

Board member Mark Rosekind asked how staff determined that the falsified charts were “intentional vs. inadvertent.” He noted the importance of this question because it represented “the beginning of the chain” of missteps that led to the crash. NTSB staff replied that a few discrepancies uncovered were “beyond coincidence,” including the altered weight documents and supplemental type certificate (STC) modifications that were reported installed, when they were not. Carson also directly acknowledged that some of the weights were not correct, according to staff. Scheuster added that investigators found eight of the 10 S-61s in use at the time with the same understatement of weight, leading them to conclude that it was not an inadvertent mistake.

Rosekind asked for further specifics in regards to the claim of intentional tampering. “Somebody took the 2.5-minute chart and pasted it over the 5-minute chart,” replied Scheuster. “You had to physically alter the chart.”

While Chairman Deborah Hersman noted that the report does not “let the pilots off the hook,” staff members stated that the crew “does not jump out as the principal causal factor in this accident.” Rosekind added that if the pilots “had the correct info, they would have been doing the right thing.”

While much of the discussion revolved around Carson’s role in the accident chain, NTSB also slammed oversight from FAA and contractor U.S. Forest Service. Hersman asked whether the FAA has the appropriate resources to catch the errors noted in the lead-up to the S-61 crash. She pointed out that while NTSB staff does not have the eye of a maintenance inspector, it took several weeks to discover the discrepancies, which were not uncovered by FAA investigators. “This is a wake up call for sure, there were some missed opportunities, but I’m not sure they’re in position to catch those opportunities today, even if they were looking for them,” Hersman said.

Others on staff and the board felt the mistakes should have been discovered prior to the accident. “Better oversight would have deterred these anomalies in the first place,” asserted Sumwalt. “There is a strong case for how better oversight could have deterred these falsifications and irregularities, as well as caught them,” he continued, adding that the board’s recommendations would seek to put further deterrents into place.

“What is the purpose of federal oversight?” Hersman asked, launching into a comparison of aviation to the bus and truck industry. In the aviation industry, “it’s like oversight among friends or something … because they’re not looking for wrongdoing, they’re just looking to check the box that the thing they were supposed to do is done.” In the truck/bus industry, there are “hundreds of thousands of more carriers of magnitude than in the aviation industry and fewer inspectors. They can’t possibly inspect everyone, and most entrants into the truck and bus industry don’t ever get an oversight activity.” But in aviation, “you actually have to get oversight before you get an operating certificate. That’s great, but in these other industries we don’t have as many resources dedicated to oversight, but you know what they do? They try to get the bad actors out, and they have to focus on the people who do the wrong things and people who are trying to make things appear as they shouldn’t.”

In almost all of NTSB’s investigations where a “bad actor” has been identified, Hersman continued, “it’s really incumbent on the oversight activity to ferret that out.” She asked whether FAA is really equipped to catch the bad actors. “Are they resourced to do that, and do they have clear enough areas of responsibility?” (From January 2011 Rotorcraft Report)
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