What Are The Differences between Service Bulletins and Airworthiness Directives?

Airworthiness DirectiveAn Airworthiness Directive (A.D.) is a directive issued when the FAA realizes that a perilous condition exists in a product (aircraft engine, airframe, appliance or propeller).  They notify aircraft operators and owners of potentially unsafe conditions that need special inspections, alterations, or repairs.

A Service Bulletin (S.B.) is a notice to an aircraft operator from a manufacturer informing him/her of a product improvement. An alert service bulletin is issued when an unsafe condition shows up that the manufacturer believes to be a safety related as opposed to a mere improvement of a product.

Service bulletins often result to issuance of Airworthiness Directives by FAA. An airworthiness directive references the alert service bulletin as a way of complying with the AD.

Having realized that there were distinct levels of seriousness to a service bulletin, manufacturers started to categorize them as optional, recommended, alert, mandatory, informational, etc. It was left to the manufacturers to classify a service bulletin as they considered best for there was no standard for the terminology.  Differentiation between non-mandatory service bulletins is done and decided only by the FAA.

Although a service bulletin may be categorized as mandatory by the manufacturer, it is crucial to know that compliance with service bulletins isn’t necessarily required under the FARs (Federal Aviation Regulations) unless the service bulletin includes or is accompanied by an airworthiness directive.

As opposed to service bulletins, airworthiness directives affect the safety conditions of a flight. It’s for this reason compliance becomes mandatory.

So, just because the FAR’s don’t necessarily demand an aircraft owner to comply with service bulletins, does this imply an aircraft owner or operator can ignore service bulletins? Not necessarily. The inaction may come back to haunt the aircraft owner at some time in the future. Therefore, it is always important to keep in mind that manufacturers issue service bulletins because they believe compliance will make their products safer.

However, compliance with service bulletins basically translates into higher costs to the aircraft owner. Whether it requires performance of a more detailed and elaborate inspection or replacement of a component, service bulletin’s recommendation simply means that the aircraft owner will dig dipper into his/her pocket in paying for labor or parts. As a result, the majority of aircraft owners reject or defer compliance with service bulletins in order to save money.

This is a usual scenario especially where the aircraft owner feels that the aircraft is safer even without compliance. In fact, if a service bulletin doesn’t have an airworthiness directive, the FAA doesn’t deem its recommendations to be mandatory or necessary. So, why should the aircraft owner pay extra costs for maintenance or parts that may not make the aircraft safer?

If safety of flights is not an alarming issue, an aircraft owner may decide to perform a cost-benefit analysis so as to compare the benefits of complying with a service bulletin and the cost of compliance. This analysis assists an aircraft owner in deciding whether to comply or not to comply with a specific service bulletin.

However, there is a way for the manufacturers to make a service bulletin regulatory for all the affected aircrafts. Requirements referred to or called out in the TCDS (Type Certificate Data Sheet) or within the airworthiness limitations part of the aircraft maintenance manual are, unexceptionally, mandatory.

The bottom line? Compliance with an A.D. is exclusively mandatory; compliance with a S.B. is not mandatory unless the service bulletin includes or is accompanied by an airworthiness directive.

7 thoughts on “What Are The Differences between Service Bulletins and Airworthiness Directives?

  1. Aaron,

    I don’t disagree with your bottom line (except to say I doubt any SB will include an AD, although the reverse is frequently true)…

    But to only mention FAA and imply that only the FAA issues ADs is rather over-simplifying the true picture.

    Please don’t make the usual US-centric error of assuming that all aviation takes place in the dear old US of A, or that it’s only the FAA who raises ADs.

    There’s a whole other world outside your lovely country, and some of us know a few things about aviation too – try replacing ‘FAA’ with ‘Airworthiness Authority relevant to the State of TC Holder or Registration’ and you’d be little closer to the truth.

    Best Wishes from one of the Mother Countries 🙂

  2. When alert service bulletins are backed up by ordinary Federal aviation regulations like FAR 91.7 and it’s global equivalents violations strike out with a vengeance. In the matter of Malaysian Airlines flight 370, bowling flagged the term structural in its alert text. The Bowing structural flag activates violation feature within FAR 91.7.
    Cockpit Culture for 12/12/2016. Causality.

    ~edited here to confirm defendant Hishamuddin Hussein 1/21/17

    “Malaysian Airlines flight #370 is a Government-sponsored Mass Murder and Cover, on a grander scale than Putin #MH17 and Gaddafi PA103.”

    I am Captain Dirck Hecking, who has more than a 33-year operating relationship on the wings and teachings of Boeing; who culls out and plagiarizes everything in the interest of justice for Malaysian Airlines victims trapped by the criminal felons below, in what has unfolded to be a murder case of one degree or another. Incorporated herein should be a claim against the defendants by the real Malaysian state.

    STATE SPONSORED CRIMINAL VIOLATIONS in the wake of blatantly false swearing claining that MH370’s loss to be an accident.

    Day by day and moment by moment, each defendant breaches duty and oath with unlawful intent and contemplated harm, in furtherance of a scheme to defraud each of you out of justice within Chapter 13 ICAO investigation… And more importantly, cover the foundation for criminal prosecutions derived therefrom.

    COUNT I – by unlawful suppression of factual information in the form of state-sponsored criminal serial violations of F A R 91.7 “no person may operate”;

    COUNT II – by unlawful suppression of Boeing’s rarest ALERT of all… Service Bulletin 777-53A0068 “corrosion and cracks” for line number 404;

    COUNT III – by unlawful suppression of factual information, the US follow on Airworthiness Directive fully backed Boeing up;

    COUNT IV – by unlawful suppression of the US Embassy’s confirmation of receiving a timely radio call, “This is Malaysia Airlines Flight 370… Cabin Disintegrating, Landing Sought”;

    COUNT V – by making Insurance false statements on Allianz claim applications… ”

    x. I point here to Malaysian indictable officials heinous acts in violation of Boeing’s Alert Service Bulletin (777-53A0068); “loss of structural integrity” warning, applicable to line numbers up to 1,202; which forced immediate grounding for mitigation, upon Malaysian Government officials in accordance with US F A R 91.7, our “structural integrity” no person may operate law. The mere movement of the fleets planes outside mitigation with the intent to fly strikes a criminal violation upon the Government owners. Certificate holders owners and operators are by duty and oath aware… the burden of proof attaches to them.

    xx. Regarding safety and fidelity, Malaysian airlines, its de facto clone M A B and the United States of America are signatories along with the EASU in matters affecting more than safety throughout mutual global aviation operations, and therefore Boeing’s rules and our rules mean something beyond borders.

    THEREFORE – I am charging Prime Minister Najib Razak, Transport Minister Liow Tiong Lai, Hishamuddin Hussein, Deputy Abdul Aziz Kaprawi and their minions (who are by duty and oath aware) for covering and breaching their duty and oath by evading compliance with airworthiness rule US FAR 91.7 (no person may operate) in the wake of Boeing’s dire shout-out about their triple 7 “Loss of structural integrity”. This is not brain surgery, every certificate holder knows this.

    BACKGROUND – Boeing served its MOST DIRE WARNING ever on Malaysian officials, 270 days before our loss. 777-53A0068.

    1) This service bulletin gives instructions to inspect for corrosion and cracks in the crown fuselage skin under 2-bay and 3-bay satellite communication (SATCOM) antenna adapter plates located in Sections 44 and 46. [Line number 404 is MH370 three bay, and Section 46… measuring 1, 601” aft of the nose] There could be fretting and damage to the fuselage skin finish due to a contact between the adapter plate bonding jumper and fuselage skin.

    2) The removal of skin finish results in exposure to corrosion, which can lead to cracks. Cracks in the fuselage skin that are not found and repaired can propagate to the point where the fuselage skin structure cannot sustain the limit load. When the fuselage skin cannot sustain limit load, this can result in possible rapid decompression and loss of structural integrity. Which syncs up with Boeing’s prophecy in the haunting last known words of Captain Shah, “This is Malaysia Flight 370…Cabin Disintegration Landing Sought”

    3) [Once informed], an operator reported a 16 inch crack under the 3-bay SATCOM antenna adapter plate in the crown skin of the fuselage between Station 1601 and STA 1622 (Section 46), and Stringer 1 Left and Stringer 2 Left on an airplane that was 14 years old with approximately 14,000 total flight cycles. The informant crack was found while doing Maintenance Planning Data (MPD) inspection, 777 MPD Section 2, 53-598-00, which requires a [bare] fuselage skin inspection between Station 1434 and STA 1832.

    4) As a part of the MPD progressive skin inspection, removal of antennas and adapter plates are necessary to access the entire fuselage skin. Subsequent to this crack finding, the same operator inspected 42 other airplanes that are between 6 and 16 years old and found some local corrosion, but no other cracking. [See 2 above, for a spot-on admission that the traits of the fatal corrosion crack propagation sequence were indeed underway in all 43 of the informants Triple 7 fleet.]

    The following one of a kind Zurich photo set shows the configuration of the cabin roof at station 1,601 on the night the plane went missing. The unique special (concerned) photo shows the aberration a maintenance man of good will would have attended to during any of the routine MPD skin inspections and during the spot on skin inspections commanded by Boeing’s ALERT SB. of June 12, 2013. NOTE: MPD inspections require all covers be removed.


    5) Boeing has performed metallurgical fracture analysis of the section of the fuselage skin with the 16-inch crack, which was sent in by the operator. The damaged fuselage skin showed that the braided section of the bonding jumper cable was contacting the skin. The contact between the bonding jumper and fuselage skin results in fretting and removal of the fuselage skin finish. The removal of finish results in exposure to corrosion.

    6) The damaged skin panel showed severe exfoliation corrosion in the area where the braided section of the bonding jumper contacted the skin. The fracture analysis showed that primary crack initiated at the area of the exfoliation corrosion. The analysis also showed that cracking progressed by intergranular stress corrosion partially through thickness for 13.5 inches along the interior surface of the skin. Further propagation of the crack through to the exterior surface occurred by fatigue.

  3. Nice post, but I didn’t understand the line “Although a service bulletin may be categorized as mandatory by the manufacturer” what does it imply?

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