(a) COMMENTS DUE DATE

    The FAA must receive comments on this airworthiness directive (AD)  by
    October 12, 2021.

(b) AFFECTED ADS

    None.

(c) APPLICABILITY

    This AD applies to all serial numbers of the airplane models listed in
    table  1 to  paragraph (c),  certificated  in  any category,  that are
    either:

(1) Modified  with a  Garmin G3X Touch Electronic Flight Instrument System
    under Supplemental Type Certificate (STC) No. SA01899WI, installed  in
    accordance with Master Drawing  List (MDL) Document No.  005-01320-00,
    Revision 9 or earlier, interfaced with a Garmin Engine Adapter GEA  24
    connected to resistive fuel probes; or

(2) Modified  with a Garmin GI 275 Multi-Function Display System under STC
    No. SA02658SE, installed in accordance with MDL Revision 9 or earlier,
    interfaced with a Garmin Engine Adapter GEA 24 connected to  resistive
    fuel probes.

Note 1 to paragraph (c):  Garmin Mandatory STC Service Bulletin  No. 2134,
Revision A, and Garmin Mandatory  STC Service Bulletin No. 2135,  Revision
A, both dated April 23, 2021, contain information for how to determine  if
your airplane has a resistive probe interface.

                TABLE 1 TO PARAGRAPH (C) — AFFECTED AIRPLANES             
    ______________________________________________________________________
    TYPE CERTIFICATE HOLDER                     AIRPLANE MODEL
    ______________________________________________________________________
    Aermacchi                S.p.A. F.260, F.260B, F.260C, F.260D, F.260E,
                             F.260F, S.205-18/F, S.205-18/R, S.205-20/F,
                             S.205-20/R, S.205-22/R, S.208, and S.208A

    Aeronautica Macchi       AM-3
    S.p.A./Aerfer-Industrie
    Aerospaziali Meridionali
    S.p.A.

    Aerostar Aircraft        PA-60-600 (Aerostar 600), PA-60-601
    Corporation              (Aerostar 601), PA-60-601P (Aerostar
                             601P), and PA-60-602P (Aerostar 602P)

    Air Tractor, Inc.        AT-401

    Alexandria Aircraft,     14-19, 14-19-2, 14-19-3, 14-19-3A, 17-30,
    LLC                      17-30A, 17-31, 17-31A, 17-31ATC, and
                             17-31TC

    Alpha Aviation Concept   R2160
    Limited

    American Champion        402, 7EC, 7ECA, 7FC, 7GC, 7GCA,
    Aircraft Corp.           7GCAA, 7GCB, 7GCBA, 7GCBC,
                             7KCAB, 8GCBC, and 8KCAB

    Aviat Aircraft Inc.      A-1, A-1A, A-1B, A-1C-180, A-1C-200, S1S,
                             S-1T, S-2, S-2A, S-2B, S-2C, and S-2S

    Bellanca Aircraft        14-13, 14-13-2, 14-13-3, and 14-13-3W
    Corporation

    B-N Group Ltd.           BN-2 and BN-2A

    The Boeing Company       AT-6 (Navy SNJ-2), AT-6A (Navy SNJ-3), AT-6B,
                             AT-6C (Navy SNJ-4), AT-6D (Navy SNJ-5),
                             AT-6F (Navy SNJ-6), BC1A, Navy SNJ-7 and T-6G

    CEAPR (type certificate  R3000/160
    previously held by
    APEX Aircraft)

    Cessna Aircraft Company  T-50 (Army AT-17 and UC-78 series, Navy
                             JRC-1)

    Cirrus Design            SR20, SR22, and SR22T
    Corporation

    Commander Aircraft       112, 112B, 112TC, 112TCA, 114, 114A,
    Corporation              114B, and 114TC

    Costruzioni              P2006T
    Aeronautiche
    Tecnam S.P.A.

    Cougar Aircraft          GA-7
    Corporation

    Cub Crafters, Inc.       CC19-180

    Daher Aircraft Design,   Kodiak 100
    LLC (type certificate
    previously held by
    Quest Aircraft Design,
    LLC)

    De Havilland Support     B.121 Series 1, B.121 Series 2, and B.121
    Limited                  Series 3

    Diamond Aircraft         DA20-A1, DA20-C1, DA 40, DA 40 F, and
    Industries Inc.          DA 40 NG

    Discovery Aviation,      XL-2
    Inc.

    Dynac Aerospace          Aero Commander Model 100, Aero
    Corporation              Commander Model 100-180, Aero
                             Commander Model 100A, Volaire Model
                             10, and Volaire Model 10A

    EADS-PZL Warszawa-       PZL-104 Wilga 80, PZL-104M Wilga 2000,
    Okecie S.A.              PZL-104MA Wilga 2000, PZLKOLIBER 150A,
                             and PZL-KOLIBER 160A

    Extra                    EA-300, EA-300/200, EA-300/L, EA
    Flugzeugproduktions-     300/LC, and EA-300/S
    und VertriebsGmbH

    FLS Aerospace (Lovaux)   OA7 Optica Series 300
    Ltd.

    Found Brothers           FBA Centennial 100
    Aviation Limited

    Frakes Aviation          G-44 (Army OA-14, Navy J4F-2)
                             (including SCAN Type 30) and G-44A

    FS 2003 Corporation      PA-12 and PA-12S

    Fuji Heavy Industries,   FA-200-160, FA-200-180, and FA-200-
    Ltd.                     180AO

    GA8 Airvan (Pty) Ltd.    GA8 and GA8-TC 320

    Gomolzig Flugzeug- und   AS 202/15 BRAVO, AS 202/18A BRAVO,
    Maschinenbau GmbH        and AS 202/18A4 BRAVO

    GROB Aircraft            SE G 115, G 115A, G 115B, G 115C, G
                             115C2, G 115D, and G 115D2

    Helio Aircraft           15A and 20
    Corporation

    Helio Alaska, Inc.       H-250, H-295 (USAF U10D), H-391 (USAF YL-24),
                             H-391B, H-395 (USAF L28A or U-10B), H-395A,
                             H-700, H-800, and HT-295

    Howard Aircraft          DGA-15J (Army UC-70B), DGA-15P (Army UC-70,
    Foundation               Navy GH-1, GH-2, GH-3, NH-1), and DGA-15W

    Interceptor Aircraft     200, 200A, 200B, 200C, 200D, and 400
    Inc.

    The King's Engineering   44 Angel, 4500-300, and 4500-300 Series II
    Fellowship

    Legend Aviation &        UC-1
    Marine, LLC

    Luscombe Aircraft        8, 8A, 8B, 8C, 8D, 8E, 8F, and T-8F
    Corporation

    Maule Aerospace          Bee Dee M-4, M-4, M-4-180C, M-4-180S,
    Technology, Inc.         M-4-180T, M-4-180V, M-4-210, M-4-210C,
                             M-4-210S, M-4-210T, M-4-220, M4-220C,
                             M-4-220S, M-4-220T, M-4C, M4S, M-4T, M-5-
                             180C, M-5-200, M-5-210C, M-5-210TC, M-5-220C,
                             M-5-235C, M-6-180, M-6-235, M-7-235, M-7-
                             235A, M-7-235B, M-7-235C, M-7-260, M-7-260C,
                             M7-420A, M-7-420AC, M-8-235, M-9-235, MT-7-
                             235, MT-7-260, MT-7-420, MX-7-160, MX-7-160C,
                             MX-7-180, MX-7-180A, MX-7-180AC, MX-7-180B,
                             MX-7-180C, MX-7-235, MX-7-420, MXT-7-160,
                             MXT7-180, and MXT-7-180A

    Micco Aircraft           MAC-125C, MAC-145, MAC-145A, and MAC-145B
    Company, Inc.

    Mooney Aircraft          M22
    Corporation

    Mooney International     M20, M20A, M20B, M20C, M20D, M20E, M20F,
    Corporation              M20G, M20J, M20K, M20L, M20M, M20R, M20S, and
                             M20TN

    Nardi S.A.               FN-333

    Pacific Aerospace Ltd.   FBA-2C, FBA-2C1, FBA-2C2, and FBA2C3

    Piaggio & C.             P.136-L and P.136-L1

    Pilatus Aircraft         PC-6, PC-6/350, PC-6/350-H1, PC-6/350-H2,
    Limited                  PC-6-H1, and PC-6-H2

    Piper Aircraft, Inc.     PA-16, PA-16S, PA-18, PA-18-105 (Special),
                             PA-18-125 (Army L-21A), PA18-135, PA-18-150,
                             PA-18A, PA-18A-135, PA-18A-150, PA-18AS-125,
                             PA-18AS135, PA-18AS-150, PA-18S, PA-18S-105
                             (Special), PA-18S-125, PA-18S-135, PA18S-150,
                             PA-19 (Army L-18C), PA-19S, PA-20, PA-20-115,
                             PA-20-135, PA-20S, PA-20S-115, PA-20S-135,
                             PA-22, PA-22-108, PA-22-135, PA-22-150, PA-
                             22-160, PA-22S-135, PA-22S-150, PA-22S-160,
                             PA-23, PA-23-160, PA-23-235, PA-23-250, PA-
                             23-250 (Navy UO-1), PA-24, PA-24-250, PA-24-
                             260, PA-24-400, PA-28-140, PA-28-150, PA-28-
                             151, PA-28-160, PA28-161, PA-28-180, PA-28-
                             181, PA-28-201T, PA-28-235, PA-28-236, PA-
                             28R180, PA-28R-200, PA-28R-201, PA-28R201T,
                             PA-28RT-201, PA-28RT-201T, PA28S-160, PA-28S-
                             180, PA-30, PA-31-300, PA-32-260, PA-32-300,
                             PA-32-301, PA32-301FT, PA-32-301T, PA-32-
                             301XTC, PA-32R-300, PA-32R-301 (HP), PA-
                             32R301 (SP), PA-32R-301T, PA-32RT-300, PA-
                             32RT-300T, PA-32S-300, PA-34-200, PA-34-200T,
                             PA-34-220T, PA-38-112, PA39, PA-40, PA-44-
                             180, PA-44-180T, PA46-310P, PA-46-350P, PA-
                             46R-350T, and PA-E23-250

    Polskie Zaklady          PZL M26 01
    Lotnicze Spolka zo.o

    Revo, Incorporated       Colonial Model C-1, Colonial Model C-2,
                             Lake Model 250, Lake Model LA-4, and
                             Lake Model LA-4-200

    Robert E. Rust, Jr.      DHC-1 Chipmunk Mk 21, DHC-1 Chipmunk Mk 22,
                             and DHC-1 Chipmunk Mk 22A

    RUAG Aerospace           Do 27 Q-6, Do 28 A-1, and Do 28 B-1
    Services GmbH

    Sierra Hotel Aero,       Navion (Army L-17A), Navion A (Army L17B and
    Inc.                     L-17C), Navion B, Navion D, Navion E, Navion
                             F, Navion G, and Navion H

    Sky Enterprises, Inc.    RC-3

    Slingsby Aviation Ltd.   T67M260

    SOCATA (type             MS 880B, MS 885, MS 892A-150, MS 892E-150,
    certificate currently    MS 893A, MS 893E, MS 894A, MS 894E, Rallye
    held by Daher)           100S, Rallye 150 ST, Rallye 150 T, Rallye
                             235C, Rallye 235 E, TB9, TB 10, TB 20, TB 21,
                             and TB 200

    Spartan Aircraft         7W (Army UC-71)
    Company

    Swift Museum             GC-1A and GC-1B
    Foundation, Inc.

    Symphony Aircraft        OMF-100-160 and SA 160
    Industries Inc.

    Textron Aviation Inc.    19A, 23, 35, 36, 50, 58, 76, 77, 95, 120,
                             140, 140A, 150, 150A, 150B, 150C, 150D,
                             150E, 150F, 150G, 150H, 150J, 150K,
                             150L, 150M, 152, 170, 170A, 170B, 172,
                             172A, 172B, 172C, 172D, 172E, 172F
                             (USAF T-41A), 172G, 172H (USAF T41A), 172I,
                             172K, 172L, 172M, 172N,
                             172P, 172Q, 172R, 172RG, 172S, 175,
                             175A, 175B, 175C, 177, 177A, 177B,
                             177RG, 180, 180A, 180B, 180C, 180D,
                             180E, 180F, 180G, 180H, 180J, 180K, 182,
                             182A, 182B, 182C, 182D, 182E, 182F,
                             182G, 182H, 182J, 182K, 182L, 182M,
                             182N, 182P, 182Q, 182R, 182S, 182T, 185,
                             185A, 185B, 185C, 185D, 185E, 190, 195,
                             195A, 195B, 206, 206H, 207, 207A, 210,
                             210-5 (205), 210-5A (205A), 210A, 210B,
                             210C, 210D, 210E, 210F, 210G, 210H,
                             210J, 210K, 210L, 210M, 210N, 210R,
                             310, 310A, 310B, 310C, 310D, 310E, 310F,
                             310G, 310H, 310I, 310J, 310J-1, 310K,
                             310L, 310N, 310P, 310Q, 310R, 320, 320-
                             1, 320A, 320B, 320C, 320D, 320E, 320F,
                             335, 336, 337, 337A, 337B, 337C, 337D,
                             337E, 337F, 337G, 337H, 340, 340A, 35-
                             33, 35-A33, 35-B33, 35-C33, 35-C33A,
                             35R, 45 (Military YT-34), 56TC, 58A,
                             58PA, 58TCA, 95-55, 95-A55, 95-B55, 95-
                             B55A, 95-B55B, 95-C55, 95-C55A,
                             A150K, A150L, A150M, A152, A185E,
                             A185F, A23, A23-19, A23-24, A23A, A24,
                             A24R, A35, A36, A36TC, A45 (Military T34A,
                             B-45), A56TC, B19, B23, B24R, B35,
                             B36TC, B50, B95, B95A, C23, C24R, C35,
                             C50, D17S, D35, D45 (Military T-34B),
                             D50E-5990, D55, D55A, D95A, E310H,
                             E310J, E33, E33A, E33C, E35, E55, E55A,
                             E95, F150F, F150G, F150H, F150J,
                             F150K, F150L, F150M, F152, F172D,
                             F172E, F172F, F172G, F172H, F172K,
                             F172L, F172M, F172N, F172P, F177RG,
                             F182P, F182Q, F33, F33A, F33C, F337E,
                             F337F, F337G, F337H, F35, FA150K,
                             FA150L, FA150M, FA152, FP172D,
                             FR172E, FR172F, FR172G, FR172H,
                             FR172J, FR172K, FR182, FRA150L,
                             FRA150M, FT337E, FT337F, FT337GP,
                             FT337HP, G17S, G33, G35, G36, G58,
                             H35, J35, K35, LC40-550FG, LC41-
                             550FG, LC42-550FG, M19A, M337B,
                             M35, N35, P172D, P206, P206A, P206B,
                             P206C, P206D, P206E, P210N, P210R,
                             P337H, P35, R172E, R172F, R172G,
                             R172H, R172J, R172K, R182, S35, SD17S,
                             T182, T182T, T206H, T207, T207A,
                             T210F, T210G, T210H, T210J, T210K,
                             T210L, T210M, T210N, T210R, T240,
                             T303, T310P, T310Q, T310R, T337B,
                             T337C, T337D, T337E, T337F, T337G,
                             T337H, T337H-SP, TP206A, TP206B,
                             TP206C, TP206D, TP206E, TR182,
                             TU206A, TU206B, TU206C, TU206D,
                             TU206E, TU206F, TU206G, U206,
                             U206A, U206B, U206C, U206D, U206E,
                             U206F, U206G, V35, V35A, and V35B

    Thrush Aircraft, LLC     600 S-2D, S2R, S2R-R1340, S2R-R1820,
                             S2R-R3S, and S2R-T34

    Topcub Aircraft, Inc.    CC18-180 and CC18-180A

    True Flight Holdings     AA-1, AA-1A, AA-1B, AA-1C, AA-5,
    LLC                      AA-5A, AA-5B, and AG-5B

    Twin Commander Aircraft  500, 500-A, 520, 560, and 560-A
    LLC

    Univair Aircraft         108, 108-1, 108-2, 108-3, 108-5, 415-C,
    Corporation              415-CD, 415-D, A-2, A2-A, E, F-1, F-1A,
                             G, and M10

    Viking Air Limited       DHC-2 Mk.I, DHC-2 Mk.II, DHC-2 Mk.III, and
                             TR-1

    Vulcanair S.p.A.         P.68, P.68 "Observer," P.68B, P.68C,
                             P.68C-TC, P.68R, P.68 Observer 2, P.68TC
                             Observer, and Vulcanair V1.0

    Waco Aircraft Company    YMF

    WACO Classic Aircraft    2T-1A, 2T-1A-1, and 2T-1A-2
    Corporation

    WSK PZL Mielec and OBR   M20 03
    SK Mielec PZL

    W.Z.D. Enterprises Inc   11A and 11E

    Zenair Ltd.              CH2000

    Zlin Aircraft a.s.       Z-143L, Z-242L, and Zlin 526L
    ______________________________________________________________________

(d) SUBJECT

    Joint  Aircraft  System  Component  (JASC)  Code  2841,  Fuel Quantity
    Indicator.

(e) UNSAFE CONDITION

    This AD was prompted by  reports of fuel quantity disparities  between
    the amount of fuel indicated and the actual amount of fuel. The FAA is
    issuing this AD  to ensure that  the amount of  fuel indicated is  the
    amount  of fuel  available. The  unsafe condition,  if not  addressed,
    could result in  fuel starvation and  engine shutdown with  consequent
    loss of airplane control.

(f) COMPLIANCE

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

(g) ACTION

    Within 100 hours time-in-service after  the effective date of this  AD
    or within  12 months  after the  effective date  of this AD, whichever
    occurs  first,  modify  the  fuel  probe  interface  by  following the
    Modification Instructions in Garmin Mandatory STC Service Bulletin No.
    2134, Revision A, or Garmin  Mandatory STC Service Bulletin No.  2135,
    Revision A, both dated April 23, 2021, whichever is applicable.

(h) ALTERNATIVE METHODS OF COMPLIANCE (AMOCS)

(1) The Manager, Wichita 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
    identified in Related Information.

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

(i) RELATED INFORMATION

(1) For more information about  this  AD,  contact  Kevin Marks,  Aviation
    Safety Engineer,  Wichita ACO Branch, FAA, 1801 Airport Road, Wichita,
    KS 67209;  phone: (316) 946-4153;  fax: (316) 946-4107;  email: kevin.
    marks@faa.gov or Wichita-COS@faa.gov.

(2) For service information identified in this AD,  contact  Garmin Inter-
    national,  Garmin Aviation Support,  1200 E 151st Street,  Olathe,  KS
    66062;  phone: (866) 739-5687;  email:  avionics@garmin.com;  website:
    https://fly.garmin.com/fly-garmin/support/.  You may view  this refer-
    enced service information at the FAA,  Airworthiness Products Section,
    Operational Safety Branch, 901 Locust, Kansas City, MO 64106.  For in-
    formation on the availability of this material at the FAA,  call (816)
    329-4148.

Issued on August 20, 2021. Lance T. Gant, Director, Compliance & Airworth-
iness Division, Aircraft Certification Service.

DATES: The FAA must receive comments  on this proposed AD  by  October 12,
2021.