STEVE ELLS delves into the history of Cherokee wing spar cracks and investigates inspection methods.
By now, every Cherokee owner, from the earliest PA-28-180 to the most recent Arrow, has heard about the inflight wing separation that occurred April 4, 2018, to a Piper Arrow owned by Embry-Riddle Aeronautical University in Daytona Beach, Florida.
A very experienced flight instructor/check airman and a student perished when the left wing of a 1997 Arrow with slightly more than 7,000 airframe hours broke off.
The NTSB issued Preliminary Report No. ERA18FA120 following the April 4, 2018, wing separation. The report said, “The airplane entered the traffic pattern and performed a touch-and-go landing.” ATC issued a transponder code and the pilot asked for approval to turn crosswind. ATC told the pilot to continue his upwind heading.
The next sentence in the NTSB report stated, “Radar data indicate the aircraft climbed to 900 feet MSL at a groundspeed of 80 knots and a heading of 240 degrees before radar contact was lost. According to multiple witness, all within 2,500 feet of the accident site, they saw the airplane flying normally, then watched as the left wing separated from the aircraft.”
Wing separation history
Unfortunately for Piper Aircraft, the FAA, and PA-28 and PA-32 owners, this is not the first wing separation in PA-28/-32 series aircraft.
The first recorded separation took place 31 years ago when the left wing of a PA-28-181 Archer II broke off.
Following that accident, Jim Burnett, Chairman of the National Transportation Safety Board, sent this letter to Donald Engen, Director of the Federal Aviation Administration:
On March 30, 1987, a Piper PA-28-181, N8191V, crashed following an in-flight separation at the wing root attachment while in cruise flight at low altitude near Marlin, Texas. The airplane, which was owned and operated by Griffin Pipeline Patrol Company, was patrolling a pipeline right of way at the time of the accident.
The pilot, the sole occupant, received fatal injuries.
Although the investigation is continuing, preliminary examination by the Safety Board’s Materials Laboratory disclosed features indicative of fatigue cracking in the separated left wing main spar. Fatigue cracking initiated at two locations just outboard of the outermost forward attachment bolt hole in the lower T-shaped spar cap of the main spar. Fatigue propagation was upward through the thickness and chordwise completely through the forward leg of the lower spar cap (about 1.3 inches). A small area of fatigue cracking also was noted in the forward web fracture piece adjacent to the forward outboard attachment bolt hole.
Examination of the left wing at the accident site disclosed evidence of an approximate 10-inch-long crack that had been stop-drilled in the upper wing skin. The crack was located forward of the main spar at the wing root and was oriented chordwise parallel to the fuselage.
The accident airplane had been flown 7,488 hours since new. Following the separation, the operator then inspected a second PA-28-181 with 7,878 hours and found upper wing skin cracks that the maintenance department had stop-drilled. When the wings were removed, a visual inspection of the spar caps at the outboard attachment hole showed “crack indications” in the same area.
The Burnett letter also included this: “Representatives of Piper Aircraft Corporation (Piper) indicate that other Piper models have wing spar structures similar to that of the PA-28.”
The NTSB issued three recommendations to the FAA:
1. Issue an airworthiness directive to require an immediate inspection of the main wing spars and upper wing skin at the wing root of Piper PA-28 airplane with over a specified number of service hours for evidence of cracking. Particular attention should be placed on inspecting the bottom surface of the lower spar cap adjacent to the outboard forward attachment bolt hole at the wing root attachment, as well as along the upper wing skin adjacent to the fuselage just forward of the main spar. (Class I, Urgent Action) (A-87-40)
2. Based on the inspection described in Safety Recommendation A-87-40, establish a recurrent periodic inspection of the wing root area for cracks by an approved method to identify those cracks before they become critical. (Class I, Urgent Action) (A-87-41)
3. Conduct a Directed Safety Investigation to inspect the lower spar cap and upper skin on other Piper model airplanes that have a similarly configured wing spar structure to that of the model PA-28 airplane. (Class I, Urgent Action) (A-87-42)AD 87-08-08 and Service Letter 997
The FAA published Airworthiness Directive 87-08-08, issued May 5, 1987, only 36 days after the wing separation.
Piper followed with Service Letter 997, issued May 14, 1987, which detailed the importance of proper wing removal procedures.
AD 87-08-08 applied to all PA-28 models, including the PA-28-201T Turbo Dakota. It also included PA-32-260 and PA-32-300 aircraft. Additionally, the AD applied to PA-28R retractable gear versions of the PA-28. The only model excluded was the PA-28-236 Dakota.
Aircraft with less than 5,000 hours total time in service (TIS) had to comply before reaching 5,050 hours; aircraft with more than 5,000 hours TIS had to comply within the next 50 hours of flight time.
The AD required that both wings be removed. One shop owner I spoke with told me than his two-man experienced crew could support the fuselage and remove both wings in 16 man-hours. His shop already had the fixtures to support the fuselage and wings. A shop doing the inspection for the first time would need to build these tools.
Compliance required a visual inspection—using a magnifying glass of at least 10 power—“for cracks in the lower spar cap from the wing skin line outboard of the outboard row of wing attach bolt holes to an area midway between the second and third row or bolt holes from the outboard row.”
The AD also mandated the use of non-destructive crack detection tools such as the dye penetrant method and eddy current testing to aid in the search for cracks.
If no cracks were found, the wings could be reinstalled.
If even the tiniest crack was found, the airplane was deemed to be unairworthy until a new spar or a wing with no spar cracks was installed.
The upper wing skins were also inspected for cracks. If found, the skin cracks had to be repaired using repair methods acceptable to the Administrator.
AD 87-08-08 did not require further inspections. Apparently, the author(s) of the AD didn’t plan for any future cracking. That assumption was incorrect.
In an effort to determine the extent of the cracking in the fleet, AD 87-08-08 also mandated that within five days of the completion of each inspection, that all inspection results be sent to the National Safety Data Branch of the FAA in Oklahoma City, Oklahoma.
AD 87-08-08 was rescinded Sept. 28, 1987, less than six months after it was issued. PA-28 and PA-32 owners and operators no longer had to pull the wings to inspect for cracks.
Piper Service Bulletin 886
On June 8, 1988, Piper Aircraft issued Service Bulletin (SB) No. 886 entitled “Wing Spar Inspection.” (This and a related Service Bulletin are available under “Magazine Extras” on the forums at PiperFlyer.org. —Ed.)
SB 886 divided the PA-28 and PA-32 airplanes into two groups.1
Group I applies to all PA-28-140 through PA-28-181 Archer II; and PA-28R-180 and PA-28R-200 Arrow II aircraft.
Group II applies to all PA-28-235 airplanes; PA-32-260 and PA-32-300; as well as all PA-28R-201 Arrow III, PA-28R-201T Turbo Arrow III and PA-28RT-201 Arrow IV and PA-28RT-201T Turbo Arrow IV aircraft.
The SB—in CAPITAL LETTERS—warns operators and owners that: “FAILURE TO FULLY COMPLY WITH THIS SERVICE BULLETIN COULD SERIOUSLY AFFECT THE STRUCTURAL INTEGRITY, SAFETY AND AIRWORTHINESS OF THE AIRCRAFT!”
It also includes this sentence: “To date, over five hundred (500) inspections have been accomplished. Only two (2) negative findings were reported on a pair of PA-32s operating in a severe environment and with considerable damage histories.”
The SB directs owners and operators to determine which “usage class” applies to their airplane.
This Service Bulletin provides instructions for:
1. determining the aircraft’s “usage class;”
2. determining the initial and recurring inspection times; and
3. accomplishing the wing spar inspection(s).
Determining aircraft usage class
The usage classes that Piper provides in SB 886 are Normal Usage (Class A), Severe Usage (Class B), Extreme Usage (Class C) and Unknown Usage (Class D).
The SB defines “normal flight training operations” as Normal Usage (Class A).
Severe Usage is defined as “aircraft which have engaged in severe usage, involving contour or terrain following operations, (such as power/pipeline patrol, fish/game spotting, aerial application, aerial advertising, police patrol, livestock management or other activities) where a significant part of the total flight time has been spent at below one thousand (1,000) feet AGL.”
Extreme Usage is defined as aircraft that have been significantly damaged, such as damage which “required major repair or replacement of wing(s), landing gear or engine mount.”
Unknown Usage is defined as “aircraft and/or wings of unknown or undetermined operational or maintenance history.”
The SB warns owners: “However, if there is any doubt as to the aircraft’s operating history, it is recommended that the initial inspection be conducted in accordance with the UNKNOWN USAGE CLASS ‘D’ Compliance Time.”
Determining inspection compliance times
Once the Usage Class has been defined, it is used to “determine the applicable initial or repetitive wing spar inspection compliance time from TABLE 1.”
The compliance times differ somewhat between Group I and Group II aircraft. Based on engineering studies completed by Piper, all Group I aircraft in the Normal Usage category must have an initial crack inspection at 62,900 hours total TIS. The aircraft must also have repetitive inspections thereafter every 6,000 hours TIS.
All Group II aircraft in the Normal Usage category must have the initial inspection at 30,600 hours TIS, and the repetitive inspections every 3,000 hours TIS.
Group I aircraft in the Severe Usage category must comply with the initial inspection requirement at 3,700 hours TIS with repetitive inspections every 1,600 hours TIS thereafter.
Group II requirements are initial at 1,800 hours TIS and repetitive inspections every 800 hours thereafter.
Interpreting this complex bulletin
The catch here is that the Piper SB says that aircraft in the Unknown Usage category should have the wings pulled to complete the initial inspection within 50 hours TIS unless the crack inspection required in AD 87-08-08 has been completed. The repetitive inspection intervals are then based on which Usage Category applies.
What this means for owners is that if the usage history prior to their purchase of the airplane is unknown, this SB, which Piper considers mandatory, requires that the wings be pulled, and the crack inspection completed right now.
I have purchased the ownership and major repair records from the FAA Aircraft Registry office—available to all owners on CD for nothing more than a phone call and less than $20—for all the airplanes I’ve owned. (For a link to the online request form, see Resources. —Ed.)
But these records only hint at how each airplane was flown prior to my ownership. Unless past ownership and flight conditions are known, an airplane is automatically in the “Unknown Usage” category.
The smoking guns
In 1987, William Johnson was an A&P mechanic and station manager for Yute Air in Dillingham, Alaska. Johnson, in addition to holding an A&P, also holds an Inspection Authorization (IA), and is an Airline Transport Pilot (ATP) with over 20,000 Alaska flying hours.
During my annual trip to the Alaska Airman’s meeting at Anchorage International Airport (PANC) in early May 2018, Johnson told me that every PA-32 that he and his crew inspected following the 1987 AD had cracks in the suspect area.
“I sent in over 40 Malfunction and Defect (M&D) reports to the FAA about cracks,” he explained during a recent phone conversation.
At the time of the AD, Yute Air was flying 4 PA-32-300 Cherokee Six 300s. In addition to changing the spars on the company Cherokees, Williams also changed spars on other western Alaska Cherokees.
Johnson told me that Ray Boyce of the FAA and a representative from Piper Aircraft visited him in Dillingham to view the results of his inspections. Comments from the FAA engineer seem to back up Johnson’s concerns that this will be a big problem.
Since it takes about 16 man-hours to remove the wings prior to the inspection, an estimate of the costs for wing removal, inspection and reattachment, assuming a $75/hour shop rate, would probably start at $3,000. This unexpected cost could be daunting to many owners.
What if there’s a way to do the inspection without removing the wings?
I wondered if an inspection panel could be cut that would expose the inspection area, so I asked this question of Paul New of Tennessee Aircraft. New is very experienced with structural repairs of Piper and Cessna aircraft.
New said there’s no way to cut an inspection hole to perform the inspection.
However, in an Investigative Update to the original NTSB Preliminary report (ERA18FA120) on the April 4 wing separation, a second Embry-Riddle flight training PA-28R-201 Arrow (Serial No. 2844135) was inspected using an eddy current inspection (ECI) method. Wing cracks were found. The second airplane had 7,661 hours TIS.
It was further reported that the cracked wings were reinstalled and subsequently inspected using a new ECI inspection procedure developed by Piper Aircraft. The new method, utilizing a bolt-hole probe inspection technique, was able to confirm the location and size of the previously identified cracks.
Based on the reported success of the bolt-hole ECI inspection, this method may be the fastest and least expensive method to inspect for wing cracks. Additionally, eddy current inspections are much more effective than dye penetrant inspections.
In every AD, there’s a paragraph saying that users are encouraged to submit alternate methods of compliance (AMOC) to solve the condition cited as causing the AD. The question now is whether there is a company that could create an eddy current inspection—or other definitive inspection technique that doesn’t require wing removal—for approval as an AMOC. Due to the equipment required and the possibility of stressing the wing structure during removal and installation, removal of the wing is the least desirable inspection mode.
In another classic case of “be careful what you pray for,” and, “behind every survivor is a lawyer,” any change to an airplane structure runs into a liability glitch.
In 1987, Cessna had stopped the manufacture of piston-powered airplanes as a statement to Congress; calling for the need for legal protection from enormous losses in civil courts. A common practice in aviation civil lawsuits to “name everyone who has deep pockets and has ever touched the airplane” meant Cessna was always listed as a defendant—even though it had not touched the subject airplane for decades, in some cases.
Piper Aircraft did not stop production, but the effects of high product liability costs contributed to the company closing its Vero Beach plant in 1990 and declaring bankruptcy in 1991.
The entire industry breathed a huge sigh of relief and celebrated Jan. 25, 1994, when Congress enacted Senate Bill 1458, also called the General Aviation Revitalization Act (GARA) of 1994. The bill was enacted to “amend the Federal Aviation Act of 1958 to establish time limitations on certain civil actions against aircraft manufacturers, and for other purposes.”
Cessna resumed production in 1996—a full nine years after it stopped production of piston-powered GA aircraft.
The most important provision of GARA was the implementation of an 18-year window of responsibility by light airplane manufacturers. This “Statute of Repose” excused Cessna (and Piper) from involvement in civil suits in accidents involving airplanes that had left the factory more than 18 years before.
However, Paragraph 2 of the Act is worded that if Cessna (or Piper, or any other light airplane manufacturer) creates a significant change and mandates the installation of that change on an airplane outside the 18-year window, the company is again subject to civil lawsuits during a new 18-year window.
In my opinion, installation of a new wing spar or installation of an airworthy used wing does not constitute a change that would reopen the statute window.
So that’s where Piper and the owners and operators of its PA-28 and PA-32 aircraft stand today. According to Piper SB 886 and 978A, if owners and operators can’t determine the usage history, a crack inspection should be performed immediately.
If cracks are found, and the aircraft is returned to airworthy status by installing a used wing, that used wing must be inspected for cracks prior to installation.
Given the gravity of a failure, and that 7,000 hours was the tipping point for the two spar failures, and that a well-maintained airplane was found to have cracks at around 7,000 hours, I strongly suggest that Piper Flyer owners start to budget for this inspection. I expect a new AD will be issued mandating inspection for cracks. Hopefully, a low-cost inspection will eliminate the need for wing removal and reinstallation to determine if cracks exist.
Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, California, with his wife Audrey. Send questions and comments to .
1 Service Bulletin 978A was issued Aug. 6, 1999 and includes serial numbers not manufactured in when SB 886 was issued. A note on page 2 of Piper Service Bulletin No. 978A reads, “This Service Bulletin is similar to Service Bulletin 886 issued June 8, 1988 with the identical purpose and has been released to add models and serial numbers not manufactured at the time of the original Service Bulletin.”
NTSB Safety Recommendation
(A-87-40, -41, -42)
Piper Aircraft Service Letter No. 997, “Wing Removal and Reinstallation”
Piper Aircraft Service Bulletin No. 886, “Wing Spar Inspection”
Piper Aircraft Service Bulletin No. 978A, “Wing Spar Inspection”
Request Copies of Aircraft Records
Piper Wing Spars Explained - Video