On October 4, 2022 the FAA issued emergency airworthiness directive (AD) 2022-21-51, which requires almost immediate inspection of the left elevator auxiliary spar of De Havilland Otter DHC-3 aircraft. While it is not known if this is related to the Northwest Seaplanes Mutiny Bay accident on September 4, 2022, ironically it was issued shortly after the wreckage of N725TH was recovered. This AD brings to light many questions of FAA activity since 2018, of which the emergency AD explicitly relates back to.

Airworthiness Directives

ADs are issued by aviation authorities in the U.S. (the FAA) and in Canada (Transport Canada, TC). They are directives to aircraft owners, operators, and maintenance providers, that action (usually some type of maintenance) is needed to make or keep aircraft safe. ADs typically arise after an aircraft or component part has an operating history of years or even decades, giving time for failure modes to develop. Once discovered that those modes could compromise safe aircraft operation, and may develop in other aircraft, ADs are issued to fix the problem or monitor the concern.   

Airworthiness Directives In Canada

Since the DHC-3 Otter type certificate holder is located in Canada, Canadian aviation regulations play an important role in ensuring the continued safe airworthiness of DHC-3 aircraft, even when they are flying in other countries including the U.S.

In Canada an airworthiness directive must be issued when “an unsafe condition exists in the aeronautical product and the condition is likely to exist or develop in other aeronautical products.” Canadian Aviation Regulations (CAR) §521.427  By law aircraft cannot operate in flight unless they are in full compliance with all applicable ADs. CAR §605.84(1)

ADs in the U.S. 

Federal law allows the FAA to accept an AD issued by TC Canada because the U.S. has a bilateral aviation safety agreement with Canada relating to aircraft certification and airworthiness. 49 USC §44701   ADs in the U.S. are governed under 14 CFR Part 39.

The FAA issues ADs when they find that “(a) an unsafe condition exists in the product; and (b) the condition is likely to exist or develop in other products of the same type design.” 14 CFR §39.5  Operating an aircraft without complying with ADs is a regulatory violation, subjecting owners and operators to certificate enforcement actions and/or civil penalty fines. 14 CFR §39.7  ADs may incorporate by reference a manufacturer’s service maintenance instructions, which become part of the AD. 14 CFR §39.27

As the October 4, 2022 emergency AD is related to inspections of the left elevator auxiliary spar, a review of the history behind the AD is warranted.

January 19, 2018 Transport Canada AD CF-2018-04

Concerned about aging aircraft and corrosion, wear, and fatigue, Transport Canada (TC) issued Airworthiness Directive (AD) CF-2018-04. “Service experience indicates that aging aircraft are more likely to be adversely affected by corrosion, wear and fatigue cracking.”

The AD recognizes that Viking Air Limited (Viking), as Type Certificate holder for the DHC-3, has developed a supplementary inspection and corrosion control program which identifies specific areas that must be inspected to ensure that corrosion, wear and fatigue-related degradation do not result in an unsafe condition. The program is documented in Viking Product Support Manual (PSM) 1-3-5 DHC-3 Otter Supplementary Inspection and Corrosion Control Manual (SICCM).

Corrosion levels are defined in PSM 1-3-5 as a means for assessing the effectiveness of the corrosion control program and recording the results of the inspections mandated by this AD.

Each item specified for inspection in PSM 1-3-5 has been substantiated to Transport Canada as having experienced significant degradation in service and, as having the potential to develop into an unsafe condition if the inspections defined in the PSM are not implemented.

Transport Canada AD CF-2018-04

The AD sets forth compliance time limits: within 18 months from the effective date of this AD, operators must accomplish all Specific Supplemental And Corrosion Inspections specified in Part 2 of SICCM PSM 1-3-5, Revision IR, dated 21 December 2017 or later revisions accepted by Transport Canada.

While the AD itself does not mention left elevator auxiliary spar, as later recognized by the FAA, that part was already covered to be inspected in the inspection and corrosion control manual, which may be incorporated by reference into the AD.  

Once issued, the FAA would have immediately been provided a copy of AD CF-2018-04. The FAA may adopt the foreign Canadian AD immediately and issue it as one of their own, or the FAA may perform its own study and analysis before acting.

Despite TC finding that the corrosion and fatigue conditions constituted an unsafe condition likely to develop in other aircraft, which came out on July 19, 2018, the FAA did not issue an AD or publicly act on CF-2018-04 for 4 years. Nor did the FAA publicly question the validity or underlying data supporting CF-2018-04.  It is not yet known why there was no action for 4 years.

February 8, 2022 FAA Issues NPRM No. 2020-1076

When the FAA finally acted on February 8, 2022, it did not issue an AD, but merely a  Notice of Proposed Rule Making (NPRM), allowing public comment and discussion before the AD became law in the U.S. In the NPRM the FAA agrees with CF-2018-04.

FAA NPRM 2020-1076 arises directly from Canadian AD CF-2018-04, of which the FAA recognized as involving “corrosion, wear, and fatigue-related degradation in aging aircraft.”  In the NPRM the FAA confirms that Transport Canada has notified it of the unsafe condition in CF-2018-04. Nearly identical to the Canadian AD, compliance with the proposed AD may be completed via compliance with the inspection program set forth by Viking Air, the type certificate holder. The FAA recognizes that the AD is needed for this “unsafe condition”, but allowed for a comment period followed by review of comments submitted. The comment period had a deadline of March 25, 2022.

The NPRM also reflects that TC substantiated each item specified for inspection by Viking “as having experienced significant degradation in service and as having the potential to develop into an unsafe condition. . .” The FAA issued the NPRM because it determined “that the unsafe condition . . is likely to exist or develop on other products of the same type design.” “This condition, if not addressed, could lead to structural failure with consequent loss of control of the airplane.”

While CF-2018-04 strictly requires compliance with Viking Air’s Product Support Manual, the proposed FAA AD would require establishing an FAA-approved method for a corrosion prevention and control program, of which PSM compliance is one approved method, but not the sole method, allowing for other alternative compliance modes. The proposed AD requires inspections to be complete within 18 months after the AD is issued. If any anomalies are noted, they are to be reported to Viking Air within 30 days. The FAA estimated cost of the proposed AD on U.S. operators is $12,325 per airplane.

The NPRM deadline for comment was March 25, 2022. A total of two comments were submitted, both from aviation mechanics in Alaska. Neither comment proposes alternative means to comply with the proposed AD. While both were against the AD, they agreed that action was needed for corrosion and fatigue inspection of aging aircraft, but that the AD was inherently unfair because it only would apply to De Havilland Otters, and not to other aging aircraft from other manufacturers.  They recommended an industry wide solution of aging aircraft inspections for all old aircraft, single and multi-engine, regardless of whether they were operating commercially or privately. There were also concerns about allowing operators to establish their own inspection program, of which the FAA must approve.

From March 25, 2022 until after the September 4 Mutiny Bay accident, there was no public action by the FAA related to this NPRM, and as reflected below, as of October 4, 2022 the FAA was still considering the two comments.

October 4, 2022 FAA Emergency AD # 2022-21-51

         As recognized by the FAA:

This emergency AD was prompted by multiple recent reports of cracks in the left-hand elevator auxiliary spar. The FAA is issuing this AD to detect and address cracks, corrosion, and previous repairs to the left-hand elevator auxiliary spar. The unsafe condition, if not addressed, could result in elevator flutter leading to elevator failure, with consequent loss of control of the airplane.

FAA Emergency AD # 2022-21-51

Corrective action in the AD requires that within 10 flight hours, or 3 days after receiving the AD, whichever occurs first, each DHC-3 Otter operating in the U.S. must “remove the left-hand elevator tab from the elevator and perform a detailed visual inspection of the entire left-hand elevator auxiliary spar for cracks, corrosion, and previous repairs.” The results of each inspection must then be reported to the FAA within 10 days.

The AD notes that this issue directly relates to Canadian AD CF-2018-04, dated January 19, 2018, which includes a requirement for inspecting elevator assemblies for corrosion. FAA AD 2022-21-51 recognizes that the FAA issued its NPR Mon February 8, 2022 in response to AD CF-2018-04, and states that the FAA “is currently addressing comments.”

It is not known why these two comments continue to hold up FAA’s overall action on NPRM No. 2020-1076, which has been an AD in Canada since January 19, 2018. However, the October 4, 2022, FAA emergency AD could be considered a partial response, but timing wise why was it issued after the Mutiny Bay accident and not well before it? If related to the accident, it was simply too late, and the FAA’s inaction needs to be investigated.

Many questions for the FAA arise:

  • Is the AD issue involving unsafe conditions with the left elevator auxiliary spar related to the Mutiny Bay Accident? If so, how?
  • When was the FAA first aware that an unsafe condition existed in the left elevator auxiliary spar of the DHC-3 Otter?
  • Why has it taken the FAA so long to look at this unsafe issue?
  • The emergency AD was issued as a result of numerous recent reports of cracks in the left elevator auxiliary spar, when and to whom were those reports made to, and did they involve any accidents?
  • Why did the FAA not issue an AD right after receiving CF-2018-04 in early 2018?
  • Was the FAA aware of (or involved with) the issuance of CF-2018-04?
  • Why did the FAA wait 4 years to take any action when they agreed that this is a safety issue that could cause planes to crash, as found by TC in early 2018?
  • Why did the FAA issue an NPRM instead of an AD in light of the known safety issue?
  • Why didn’t the FAA act on the NPRM sooner, especially shortly after the March 25, 2022 comment period expired, and there were only two comments?
  • When is the FAA going to complete its “comments” review of the NPRM and properly issue a complete AD covering all of the CF-2018-04 inspections, and not just the left elevator auxiliary spar?
  • What is the FAA doing about safety issues involving aging aircraft?
  • Why do the regulations (14 CFR §135.422) only require aging airplane inspections for multi-engine airplanes used in commercial service, and do not address single engine aircraft used in commercial service, nor all aircraft used in private service?

Full text of the Emergency AD can be found below: