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2019-08-51 CIRRUS DESIGN CORPORATION:
( e m e r g e n c y )

Product Identifier 2019-CE-020-AD.

(a) EFFECTIVE DATE

    This Emergency AD is effective upon receipt.

(b) AFFECTED ADS

    None.

(c) APPLICABILITY

    This AD applies to Cirrus Design Corporation Model SF50 airplanes, all
    serial numbers, certificated in standard category.

(d) SUBJECT

    Joint Aircraft System Component (JASC)/Air Transport Association (ATA)
    of America Code 27; Flight Controls.

(e) UNSAFE CONDITION

    This AD was prompted by Cirrus reporting three incidents of the  stall
    warning  and  protection  system  (SWPS)  or  Electronic  Stability  &
    Protection (ESP) System  engaging when not  appropriate. The SWPS  and
    ESP  may engage  even  when  sufficient airspeed  and proper  angle of
    attack (AOA) exists for normal flight. SWPS includes the stall warning
    alarm,  stick  shaker  and  stick  pusher.  ESP  includes  under speed
    protection (USP). The SWPS  and ESP engaging could  potentially result
    in a STALL WARNING crew alert (CAS) message activation, accompanied by
    an  audio  alarm and  stick  shaker activation,  followed  possibly by
    either low speed  ESP/USP engaging and/or  the stick pusher  engaging.
    The pilot will also observe the dynamic and color-coded (Red) airspeed
    awareness  ranges  displaying  the stall  band,  regardless  of actual
    indicated airspeed. These conditions,  if not addressed, could  result
    in the flight crew having difficulty controlling the airplane, lead to
    excessive nose-down attitude, significant altitude loss, and  possible
    impact with terrain.

(f) COMPLIANCE

    Comply  with this  AD within  the compliance  times specified,  unless
    already done.

(g) CORRECTIVE ACTION

(1) Before further flight after receipt of this emergency AD,  replace the
    AOA sensor with an improved AOA sensor, Aerosonic part number  4677-03
    Mod 1 or Cirrus part  number 32159-004 in accordance with  section 11.
    ACCOMPLISHMENT INSTRUCTIONS, paragraphs A,  B, and C of  Cirrus Design
    Corporation SF50 Service Bulletin Number: SB5X-34-03,  dated April 16,
    2019.

(2) Before further flight  after  replacement  of the AOA sensor per para-
    graph (g)(1) of this AD,  perform  final  installation  checkout  pro-
    cedures and flight tests in  accordance with a method approved  by the
    Manager,  FAA, Chicago  ACO Branch.  For the  checkout procedures  and
    flight test to be approved by the Manager, FAA,  Chicago ACO Branch as
    required  by  this  paragraph,  the  Manager’s  approval  letter  must
    specifically refer to this AD.

(3) As of the effective date of this emergency AD,  do not install any AOA
    sensor on any affected airplane unless it is an improved AOA sensor as
    identified in paragraph (g)(1) of this AD.

(h) SPECIAL FLIGHT PERMIT

    A  special flight  permit is  allowed with  the following  limitation:
    Operators   may   fly   the  airplane   to   a   location  where   the
    modification/corrective action can be incorporated. However, the pilot
    must  follow  the  procedures  listed  in  section  4.,  Pilot Actions
    Required, in Cirrus SF50  Alert Service Advisory SA19-08,  dated April
    8, 2019.

(i) ALTERNATIVE METHODS OF COMPLIANCE (AMOCS)

(1) The  Manager,  Chicago ACO Branch,  FAA,  has the authority to approve
    AMOCs for this AD,  if requested  using the procedures found in 14 CFR
    39.19.  In accordance with 14 CFR 39.19,  send  your  request  to your
    principal  inspector  or  local  Flight Standards District Office,  as
    appropriate.  If sending information directly  to  the  manager of the
    certification  office,  send it to the attention of the person identi-
    fied in paragraph (j)(1) of this AD.

(2) Before using any approved AMOC,  notify your appropriate principal in-
    spector,  or  lacking a principal inspector,  the manager of the local
    flight standards district office/certificate holding district office.

(j) RELATED INFORMATION

(1) For further information about this AD, contact: Wess Rouse, Small Air-
    plane Program Manager,  2300 East Devon Avenue, Room 107, Des Plaines,
    Illinois 60018; telephone: (847) 294-8113; fax: (847) 294-7834; email:
    wess.rouse@faa.gov.

(2) For copies of the service information referenced in this AD,  contact:
    Cirrus Worldwide Headquarters,  4515 Taylor Circle, Duluth, Minnesota,
    55811;  telephone: (800) 921-2737 or after hours (800) 921-2737;  fax:
    (218) 788-3500; email fieldservice@cirrusaircraft.com; Internet https:
    //cirrusaircraft.com/service-support/.  You may  view  this referenced
    service information at the FAA,  Small Airplane Standards Branch,  901
    Locust, Kansas City, Missouri 64106. For information on the availabil-
    ity of this material at the FAA, call (816) 329-4148.

Issued in Kansas City, Missouri, on April 18, 2019. Lance T Gant, Director
Compliance & Airworthiness Division, Aircraft Certification Service.
PREAMBLE 

DATE: April 18, 2019
AD #: 2019-08-51

Emergency Airworthiness Directive (AD) 2019-08-51 is sent to owners and operators of Cirrus Design Corporation (Cirrus) Model SF50 airplanes.

Background

This emergency AD was prompted by Cirrus reporting three incidents on Cirrus Model SF50 airplanes of the stall warning and protection system (SWPS) or Electronic Stability & Protection (ESP) System engaging when not appropriate, with the first incident occuring in November 2018 and the latest in April 2019. The SWPS or ESP systems may engage even when sufficient airspeed and proper angle of attack (AOA) exists for normal flight. The SWPS includes the stall warning alarm, stick shaker, and stick pusher. The ESP includes under speed protection (USP). The SWPS system engaging inappropriately could potentially result in a STALL WARNING crew alert (CAS) message activation, accompanied by an audio alarm and stick shaker activation, followed possibly by either low speed ESP/USP engaging, and/or the stick pusher engaging. The pilot will also observe the dynamic and color-coded (Red) airspeed awareness ranges displaying the stall band, regardless of actual indicated airspeed.

The information below presents information on each incident.

1. While the airplane was under manual pilot control, the airplane activated several downward pitch commands coincident with stall warning, stick shaker, and several associated alerts. The pilot reported "AOA FAIL" and "STICK PUSHER FAIL CAS" messages preceding the pitch command. The pilot was able to stop the automatic pitch commands by pressing and holding the autopilot disconnect button in accordance with the emergency procedure in the airplane flight manual and safely landed at his destination.

2. The operator reported stall warning and stick pusher failure in flight.

3. The airspeed indicator went red and the stall warning and stick shaker were heard and felt while on descent. The autopilot was disengaged with the same results. The system settled with stick pusher fail, stall warning fail, and low speed awareness (LSA) fail under the airspeed. The pilot hand flew the approach and had no VREF indicator but AOA appeared to be operating normally.

Cirrus and Aerosonic (manufacturer of the technical standard order AOA sensor) have identified the probable root cause as an AOA sensor malfunction due to a quality escape in the assembly of the AOA sensor at Aerosonic. Two set screws that secure the potentiometer shaft to the AOA vane shaft may have improper torqueing and no application of thread locker (Loctite) to secure the two set screws. The AOA sensor with this quality escape is labeled with part number 4677-03.

Potential erroneous AOA derived indications may occur before, during, and after unintended
automatic control system engagement. These indications include an abnormal appearing low speed red band or VREF green donut presented on the airspeed tape. Failed indications or intermittent indication may result in one or more of the following:

• Unintended automatic flight control activations;

• The flight crew having difficulty controlling the airplane;

• Excessive nose-down attitude; and/or

• Possible impact with terrain.

Relevant Service Information


We reviewed Cirrus Design Corporation SF50 Service Bulletin Number: SB5X-34-03, dated
April 16, 2019 (SB5X-34-03). The service information provides instructions for replacing the AOA sensor with an improved flight sensor.

FAA’s Determination

We are issuing this AD because we evaluated all the relevant information and determined the
unsafe condition described previously is likely to exist or develop in other products of the same type design. The noted condition presents an immediate danger to pilots and passengers of Cirrus Design Corporation Model SF50 airplanes because an uncommanded pitch down may be difficult to recover from in some flight regimes with potential fatal consequences. The before further flight compliance time and need to replace the AOA sensors due to the potential fatal consequences does not allow for prior notice and opportunity to comment for the public.

AD Requirements

This AD requires replacing the AOA sensors with improved AOA sensors using the
instructions in SB5X-34-03.

Differences Between This AD and the Service Information

SB5X-34-03 specifies 5 hours time-in-service (TIS) before replacing the AOA sensors. We
determined that allowing 5 hours TIS to replace the AOA sensors does not mitigate the unsafe
condition; thus, this AD requires such replacement before further flight.

Authority for this Rulemaking

Title 49 of the United States Code specifies the FAA’s authority to issue rules on aviation
safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII,
Aviation Programs, describes in more detail the scope of the Agency’s authority.

We are issuing this rulemaking under the authority described in Subtitle VII, Part A,
Subpart III, Section 44701, "General requirements." Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

Presentation of the Actual AD


We are issuing this AD under 49 U.S.C. Section 44701 according to the authority delegated to me by the Administrator.