# N107ML: 2012 Air Tractor AT-402B - Status: Valid registration - Airframe: [Air Tractor AT-402B](https://openairdocs.org/model/air-tractor-at-402b) (registry code 0390208, 2 seats) - Engine: [Pratt & Whitney Canada PT6A-34AG](https://openairdocs.org/engine/pratt-whitney-canada-pt6a-34ag) (registry code 52251) - Data sheets: [TCDS A17SW](https://openairdocs.org/tcds/A17SW) (Air Tractor Inc.), [TCDS E4EA](https://openairdocs.org/tcds/E4EA) (Pratt & Whitney Canada Corp.) (OpenAirDocs) - Serial number: 402B-1250 - Year built: 2012 - Type: Fixed wing single engine - Engine type: Turbo-prop - Airworthiness: Restricted, agriculture and pest control, forest - Airworthiness date: March 1, 2012 - Certificate issued: February 12, 2024 - Expires: February 28, 2031 - Mode S code: A01FD3 - Registered owners: [Mike Ogan Farms](https://openairdocs.org/faa-owner/MIKE%20OGAN%20FARMS), [Ogan Justin](https://openairdocs.org/faa-owner/OGAN%20JUSTIN), [Ogan Mike](https://openairdocs.org/faa-owner/OGAN%20MIKE), [Ogan Colin](https://openairdocs.org/faa-owner/OGAN%20COLIN), [Ogan Patty](https://openairdocs.org/faa-owner/OGAN%20PATTY) - Location: [Pierre, SD](https://openairdocs.org/faa-place/SD/Pierre) - Owner type: Partnership - Owner's area on the map: 44.5276° N, 100.3091° W: Placed by OpenAirDocs at the center of ZIP code 57501, within about 13 miles (OpenAirDocs). The owner's mailing address, not where the aircraft is based - FAA registry: https://registry.faa.gov/AircraftInquiry/Search/NNumberResult?nNumberTxt=107ML - Page: https://openairdocs.org/aircraft/N107ML From the FAA registry file of October 24, 2026. ADs below are matched by the registry's airframe and engine model codes. They may apply; each AD's applicability can narrow it by serial number, part number or installed equipment. This is not a compliance determination. ## ADs that may apply (OpenAirDocs): 17 in force ### Matched by airframe (Air Tractor AT-402B) - [AD 2021-05-14](https://openairdocs.org/ad/2021-05-14): TE flap control system · Air Tractor AT-250, AT-300, AT-301 and 19 more. Effective Apr 29, 2021 - [AD 2009-11-05](https://openairdocs.org/ad/2009-11-05): Cracks in the engine mount · Air Tractor AT-400, AT-400A, AT-402 and 9 more. Effective Jun 1, 2009 - [AD 2006-08-08 R1](https://openairdocs.org/ad/2006-08-08-R1): Wing lower spar cap · Winglets (Aero Spraying Service STC SA00490LA). Effective May 5, 2009 - [AD 2008-26-01](https://openairdocs.org/ad/2008-26-01): Overturn skid plate kit · Air Tractor AT-250, AT-300, AT-301 and 15 more. Effective Jan 28, 2009 - [AD 2008-21-08](https://openairdocs.org/ad/2008-21-08): Rudder and vertical fin hinge · Air Tractor AT-402, AT-402A and AT-402B. Effective Nov 20, 2008 - [AD 2005-13-12](https://openairdocs.org/ad/2005-13-12): Front and rear spar of the horizontal stabilizer · Air Tractor AT-300, AT-301, AT-302 and 11 more. Effective Aug 5, 2005 - [AD 2004-15-15](https://openairdocs.org/ad/2004-15-15): Aft Fuselage Upper Longeron · Air Tractor AT-401, AT-401B, AT-402 and 10 more. Effective Sep 7, 2004 - [AD 2003-07-04](https://openairdocs.org/ad/2003-07-04): Vertical Fin Front Spar Fittings · Air Tractor AT-300, AT-400, AT-400A and 8 more. Effective May 22, 2003 - [AD 98-25-01](https://openairdocs.org/ad/98-25-01): Flap Actuator Overtravel Stop · Air Tractor AT-300, AT-301, AT-302 and 13 more. Effective Jan 19, 1999 ### Matched by engine (Pratt & Whitney Canada PT6A-34AG) - [AD 2022-08-13](https://openairdocs.org/ad/2022-08-13): Turbine Section · Pratt & Whitney Canada PT6A-34, PT6A-34B, PT6A-34AG and 2 more. Effective May 27, 2022 - [AD 2014-11-05](https://openairdocs.org/ad/2014-11-05): Reinforcement liner to the power turbine (PT) containment ring and, for certain PT containment rings, adding scallops · Pratt & Whitney Canada PT6A-11, PT6A-110, PT6A-112 and 18 more. Effective Aug 5, 2014 - [AD 2011-25-12](https://openairdocs.org/ad/2011-25-12): Sun gear · Pratt & Whitney Canada PT6A-15AG, PT6A-27, PT6A-28 and 4 more. Effective Dec 28, 2011 - [AD 2011-20-51](https://openairdocs.org/ad/2011-20-51): Gears · Pratt & Whitney Canada PT6A-15AG, PT6A-27, PT6A-28 and 4 more. Effective Nov 1, 2011 - [AD 2002-23-13](https://openairdocs.org/ad/2002-23-13): Turbine Exhaust Ducts · Pratt & Whitney Canada PT6A-11, PT6A-110, PT6A-112 and 20 more. Effective Dec 31, 2002 - [AD 97-04-12](https://openairdocs.org/ad/97-04-12): Compressor Bleed-off Valve · Pratt & Whitney Canada PT6A-11, PT6A-110, PT6A-112 and 52 more. Effective Mar 14, 1997 - [AD 90-12-05](https://openairdocs.org/ad/90-12-05): Engine Overhaul · Pratt & Whitney Canada PT6A-15AG, PT6A-27, PT6A-28 and 3 more. Effective May 30, 1990 - [AD 80-08-12](https://openairdocs.org/ad/80-08-12): Fuel Pump Drive Coupling Splines · Pratt & Whitney Canada PT6A-11, PT6A-112, PT6A-135 and 24 more. Effective Apr 18, 1980 ### Historical (superseded or no longer in force) - [AD 2008-11-17](https://openairdocs.org/ad/2008-11-17) (historical): Overturn skid plate in the cockpit area · Air Tractor AT-250, AT-300, AT-301 and 14 more. Effective Jul 7, 2008 - [AD 2008-10-12](https://openairdocs.org/ad/2008-10-12) (historical): Cracks in the engine mount · Air Tractor AT-400, AT-400A, AT-402 and 9 more. Effective Jun 12, 2008 - [AD 2006-08-08](https://openairdocs.org/ad/2006-08-08) (historical): Wing lower spar cap · Air Tractor AT-400, AT-401, AT-401B and 3 more. Effective Apr 21, 2006 - [AD 2002-19-10](https://openairdocs.org/ad/2002-19-10) (historical): Upper longeron and upper diagonal tube · Air Tractor AT-402, AT-402A, AT-402B and 3 more. Effective Nov 15, 2002 - [AD 2002-11-05](https://openairdocs.org/ad/2002-11-05) (historical): Wing Lower Spar Cap · Winglets (Aero Spraying Service STC SA00490LA). Effective Jul 12, 2002 - [AD 2001-10-04 R1](https://openairdocs.org/ad/2001-10-04-R1) (historical): Wing Lower Spar Cap · Air Tractor AT-400, AT-400A, AT-401 and 11 more. Effective Jun 8, 2001 - [AD 2001-10-04](https://openairdocs.org/ad/2001-10-04) (historical): Wing Lower Spar Cap · Air Tractor AT-400, AT-401, AT-401B and 10 more. Effective Jun 8, 2001 - [AD 96-23-19](https://openairdocs.org/ad/96-23-19) (historical): Flap Actuator Overtravel Stop · Air Tractor AT-300, AT-301, AT-302 and 13 more. Effective Dec 18, 1996 ## Information bulletins (advisory) (7 in force) - [SAIB CE-18-06](https://openairdocs.org/saib/CE-18-06): Flight Controls, Rudder Control System. Issued Dec 1, 2017 - [SAIB CE-16-27](https://openairdocs.org/saib/CE-16-27): Flight Controls, Trailing Edge (TE) Flap Control System. Issued Oct 31, 2016 - [SAIB CE-16-10](https://openairdocs.org/saib/CE-16-10): Stabilizers, Rudder Structure. Issued Dec 1, 2015 - [SAIB CE-11-57](https://openairdocs.org/saib/CE-11-57): Powerplant, Engine Mount Section. Issued Sep 14, 2011 - [SAIB CE-11-41](https://openairdocs.org/saib/CE-11-41): Fuselage, Wing Attach Fittings. Issued Jun 29, 2011 - [SAIB CE-11-30](https://openairdocs.org/saib/CE-11-30): Aircraft Structures. Issued May 9, 2011 - [SAIB NE-12-04](https://openairdocs.org/saib/NE-12-04): Turbine/ Turboprop Engine: Reduction Gearbox. Issued Nov 1, 2011 ## NTSB investigations (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB CEN25LA221](https://openairdocs.org/ntsb/CEN25LA221), Jun 24, 2025: Air Tractor AT-402B (N107ML), Pierre, SD, substantial damage. Probable cause: The pilot’s failure to maintain clearance with the power lines while maneuvering that resulted in an in-flight collision with the power lines and impact with terrain. ## FAA accident and incident reports (1) From the FAA Accident/Incident Data System. Reports are matched to registry aircraft by N-number and event date, checked against the reported make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [Accident 20250624006999A](https://openairdocs.org/incident/20250624006999A), Jun 24, 2025: Air Tractor Inc AT-402B (N107ML), Pierre, SD, Substantial damage. Local family farm pilot son & part [privacy data omitted] of aircraft was spraying their farm field under a high-tension power line. Attempted to climb over… ## Service difficulty reports None filed for this aircraft. Matched to this aircraft by N-number and event date, checked against the reported serial number, make and model. ## Service difficulty reports on N107ML not matched to an aircraft (10) They name N107ML, but no registry record covers the date, the aircraft registered then was built later, or the report describes another aircraft. - [SDR JBXA000282](https://openairdocs.org/sdr/JBXA000282), May 26, 2001: TRANSMITTER. FAILED. EN ROUTE FROM PHL TO DCA, PLANE RECEIVED A LIGHTNING SRIKE TO LEFT HAND SIDE OF PLANE. CREW RECEIVED A LOW OIL PRESSURE WARNING AND NR 1 ENGINE SHUT DOWN. CAPTA - [SDR JBXA000274](https://openairdocs.org/sdr/JBXA000274), Apr 30, 2001: WARNING SYSTEM. ACTIVATED. AFTER TAKEOFF GRD/FLT FAULT STALL CMPTR FAULT LIFT DUMPER FAULT. PERFORMED OPERATIONAL CHECK OF PSEU IAW F-100 AMM 31-41-00 NO FAULTS NOTED. CYCLED GROUND FLIGH - [SDR JBXA000231](https://openairdocs.org/sdr/JBXA000231), Dec 26, 2000: COMPUTER. FAILED. DISCREPANCY: AFTER TAKEOFF HAD LIFT DUMPER FAULT, GROUND FLIGHT CONTROL, STALL COMPUTER FAIL MESSAGE. FOLLOWED BY TCAS FAULT LEVEL 3 WARNING TAKEOFF CONFIG, AND - [SDR JBXA000200](https://openairdocs.org/sdr/JBXA000200), Aug 31, 2000: WARNING LIGHT. ILLUMINATED. LIFTDUMPER FAULT OCCURRED DURING TAKE-OFF CONFIGURATION, CHECK ON END OF RUNWAY. AIRCRAFT RETURNED TO THE GATE. MX CYCLED CIRCUIT BREAKER. CLEARED LIFTDUMPER (S - [SDR JBXA0000135](https://openairdocs.org/sdr/JBXA0000135), Jan 3, 2000: TRANSDUCER. BROKEN. FLT NR 45 RDU/FLL, UPON INITAL TAKEOFF ROLL, THE STICK SHAKER ACTIVATED AND STALL COMPUTER ANNUNCIATED ON LEFT MFDU. FOUND LEFT AOA VANE BROKEN. REMOVED AND REP - [SDR JBXA980044](https://openairdocs.org/sdr/JBXA980044), Jul 7, 1998: SENSOR. MALFUNCTIONED. AIRCRAFT WAS LANDING AT MCO WHEN THE CREW RECEIVED APU FIRE WARNING. DISPATCHED THE BOTTLE. UPON LANDING, MAINTENANCE INSPECTED THE AIRCRAFT, NO SIGNS OF FIRE. - [SDR JBXA980041](https://openairdocs.org/sdr/JBXA980041), Jun 18, 1998: FIRE DETECTOR. MALFUNCTIONED. ON FINAL APPROACH TO RDU, STARTED APU AND WHILE IN START CYCLE APU FIRE WARNING CAME ON. DISCHARGED FIRE BOTTLE. INSPECTION OF APU ENCLOSURE AND APU AREA REVEAL - [SDR JBXA970026](https://openairdocs.org/sdr/JBXA970026), Nov 26, 1997: COMPRESSOR. FAILED. RDU - FLT 2 - AFTER DEPARTURE AT RDU TO PBI NR 2 ENGINE HAD 2 LOUD BANG NOISES THEN THE N2 VIBRATION WENT TO THE TOP OF THE GREEN ARC. AFTER THE 2 NOISES THER W - [SDR JBXA00028](https://openairdocs.org/sdr/JBXA00028), Nov 15, 1996: WARNING LIGHT. ILLUMINATED. BDL - FLT 373 - AIRCRAFT STARTED TAKEOFF ROLL, HAD A STAB NR 1 AND NR 2 FAULT. PLANE RETURNED TO GATE. MAINTENANCE PERFORMED AFCAS TEST. AIRCRAFT RETURNED TO SE - [SDR JBXA00020](https://openairdocs.org/sdr/JBXA00020), Oct 18, 1996: DEICE SYST. MALFUNCTIONED. DCA - WHILE EN ROUTE, AIRCRAFT PUT IN HOLD BY ATC. ICING CONDITIONS ENCOUNTERED. ENGINE ONE VIBRATION GAUGE WENT INTO AMBER AND ABOVE WHILE IN ICING CONDITIONS. ## STCs that may be installed (OpenAirDocs) (67, first 50) Approved for this aircraft's airframe or engine model, in force first, then newest. The registry doesn't record which STCs an aircraft has; its records do. ### Approved for the airframe (Air Tractor AT-402B) - [STC SA04484CH](https://openairdocs.org/stc/SA04484CH): Installation of a Reabe Aircraft Improvement Power Gate Control System. Reabe Design LLC - [STC SA01800SE](https://openairdocs.org/stc/SA01800SE): Fabrication and installation of new or replacement of existing instrument panel lights dimmer control. TCW Technologies, LLC - [STC SA01861SE](https://openairdocs.org/stc/SA01861SE): Fabrication and installation of Landing Light Controller. TCW Technologies, LLC - [STC SA04837NY](https://openairdocs.org/stc/SA04837NY): Installation of AeroLED's Holdings, LLC., position lights, navigation lights, strobe lights and beacon lights. AeroLED's Holdings, LLC - [STC SA02019SE-D](https://openairdocs.org/stc/SA02019SE-D): Installation of Garmin Model GTN 625/635/650; 725/750 Navigation System. Garmin International Inc - [STC SA09719AC](https://openairdocs.org/stc/SA09719AC): Installation electrostatic spray equipment and controls. Zee Systems Inc - [STC SA12204WI](https://openairdocs.org/stc/SA12204WI): Wing Spar Cap manufacturing process change. Air Tractor Inc - [STC SA03040CH](https://openairdocs.org/stc/SA03040CH): Installation of a digital payload hopper quantity and spray boom pressure indicating system. Reabe Design LLC - [STC SA12083IB](https://openairdocs.org/stc/SA12083IB): Installation of the Avia Propeller Ltd. model V508H/108/A propeller. MT-Propeller Entwicklung GmbH - [STC SA02738CH](https://openairdocs.org/stc/SA02738CH): Installation of L-3 Communications Avionics Systems. Acron Aviation Inc - [STC SA04046CH PAGE 1](https://openairdocs.org/stc/SA04046CH%20PAGE%201): Installation of L-3 GENESIS (TM) Electronic Standby Instrument System (ESI-500/MAG-500). Acron Aviation Inc - [STC SA01240SE](https://openairdocs.org/stc/SA01240SE): Installation of secondary voltage indication system. Visual Instruments LLC - [STC SA01995WI](https://openairdocs.org/stc/SA01995WI): Spray System Installation. See attached FAA Approved Model List (AML) SA01995WI for required data. Aeronautix, LLC - [STC SA04676CH](https://openairdocs.org/stc/SA04676CH): Installation of a True Quantity Gauge System. Reabe Design LLC - [STC SA01851WI](https://openairdocs.org/stc/SA01851WI): Installation of a Hydraulic Actuator and Auger. Texas Transland LLC - [STC SA02266SE](https://openairdocs.org/stc/SA02266SE): Installation of a Lever Throttle Quadrant. Kawak Aviation Technologies Inc - [STC SA02444AK](https://openairdocs.org/stc/SA02444AK): Approval of the L-3 Communications NGT 9000/9000R ADS-B system installed. ADS-B Technologies LLC - [STC SA00888SE](https://openairdocs.org/stc/SA00888SE): Option 1: Install Walter M601-E11S engine and a Hartzell HC-B3TW-3/T10282N+4 propeller or a Walter M601-E11 engine and an Avia V508-E-AG 106/A propeller per the Master Drawing List and Installation Instructions given in Approved Model List SA00888SE. (Note: Prior to July 17, 2002, the model M601-E11S engine was designated as the model M601-E11 engine). Option 2: Install a Walter M601-D11 engine and Avia V508-E-AG 106/A propeller per Cascade Flying Service Master Drawing List CFS-MDL-0001 Rev G, dated June 15, 2004, and Cascade Flying Service Document CFS-IM-107, Rev A, dated July 29, 2003, “Installation Instructions for Walter Turbine Installation on Air Tractor 300 & 400 Series Ag Aircraft,” or later FAA-approved revisions to these documents. NOTE: The Air Tractor model AT-400, AT-402B, AT-502, AT-502B, and AT-503A airplanes are not eligible for modification under option 2. Cascade Flying Service LLC - [STC SA01714WI](https://openairdocs.org/stc/SA01714WI): Installation of a Garmin transponders: (a) GTX 330/330D/33/33D with ADS-B Out functionality; (b) GTX 335/335R/345/345R with ADS-B Out and In functionality; or (c) GTX 335R/345R with ADS-B Out functionality in select airplanes installed with G950/G1000 systems. Garmin International Inc - [STC SA00344BO PAGE 2](https://openairdocs.org/stc/SA00344BO%20PAGE%202): Installation of Parmetheus Plus LED PAR36 and PAR46 taxi and landing lights. Whelen Aerospace Technologies - [STC SA02135SE](https://openairdocs.org/stc/SA02135SE): Installation of Electronics International Inc. Glass Panel Engine Monitor (with In-Flight Data). Electronics International Inc - [STC SA04165NY](https://openairdocs.org/stc/SA04165NY): Installation of Latitude Technologies Skynode S200 Satcom system must be performed. Latitude Technologies Corporation - [STC SA01435SE](https://openairdocs.org/stc/SA01435SE): Installation of J.P. Instruments (JPI) Primary Engine Data Management System. J. P. Instruments - [STC SA01323CH](https://openairdocs.org/stc/SA01323CH): Installation of a ground single point fueling system. Turbine Conversions Ltd - [STC SA04145NY](https://openairdocs.org/stc/SA04145NY): Installation of the Flight Data Acquisition Storage and Transmission System (Fast). Amtech Aeronautical Limited - [STC SA00905SE](https://openairdocs.org/stc/SA00905SE): Install modified engine cowl. Cascade Flying Service LLC - [STC SA02205SE](https://openairdocs.org/stc/SA02205SE): Installation of a replacement airframe fuel pump in accordance with Cascade Flying Service Master Drawing List FW-CFS545-90, Rev. B, dated October 19, 2011, or later FAA approved revision. Cascade Aircraft conversions LLC - [STC SA01745WI](https://openairdocs.org/stc/SA01745WI): Installation of a Cable Cutter System on the Main Landing Gear. Hershey Flying Service Inc - [STC SA01845WI](https://openairdocs.org/stc/SA01845WI): Installation of a Center Windshield. Hershey Flying Services - [STC SA00382BO](https://openairdocs.org/stc/SA00382BO): Installation of Globalstar Antenna and Cradle provisions to support a Globalstar GPS-1700 in non-composite airplanes. Avidyne Corporation - [STC SA02276AK](https://openairdocs.org/stc/SA02276AK): Installation of AMSAFE Aviation Inflatable Restraints. AMSAFE Inc - [STC SA02119SE PAGE 1](https://openairdocs.org/stc/SA02119SE%20PAGE%201): Installation of Garmin GDL 88 ADS-B UAT Transceiver System. Garmin International Inc - [STC SA03439CH](https://openairdocs.org/stc/SA03439CH): Installation of a Hartzell Propeller model .HC-B4TN-3C/T10702NS (4 Blade). Aero Innovations LLC - [STC SA02442AK PAGE 1](https://openairdocs.org/stc/SA02442AK%20PAGE%201): Approval of the L-3 Communications NGT 2000/2500 ADS-B system. ADS-B Technologies, LLC - [STC SA00490LA](https://openairdocs.org/stc/SA00490LA): Installation of winglets. Aero Spraying Service Inc - [STC ST03554CH](https://openairdocs.org/stc/ST03554CH): Installation of Rotary Gatekeeper and provisions equipment. Turbine Conversions Ltd - [STC SA00403SE](https://openairdocs.org/stc/SA00403SE): Installation of Vortex Generators on the wings. Micro AeroDynamics Inc - [STC SA00432SE](https://openairdocs.org/stc/SA00432SE): Installation of EGT 701 series fuel flow instrument. J P Instruments - [STC SA00861SE](https://openairdocs.org/stc/SA00861SE): Installation of J.P. Instruments (JPI) fuel flow indicating system. J P Instruments - [STC SA03199CH](https://openairdocs.org/stc/SA03199CH): Install auto fill fuel system. Wilbur-Ellis LLC - [STC SA01583CH](https://openairdocs.org/stc/SA01583CH): Installation of a Trace Engines, LP OE600A model engine, McCauley 3FF34C529/106AW[X]-0 model propeller and associated systems. Trace Engines LP - [STC SA02985CH](https://openairdocs.org/stc/SA02985CH): Installation of a Cool Start System in accordance with Installation Instructions , Revision A, dated April 14, 2011, or later FAA Approved revision. Turbine Conversions Ltd - [STC SA00068SE](https://openairdocs.org/stc/SA00068SE): Installation of fuel flow/pressure instruments. (W/TSIO-360-MB1). Electronics International Inc - [STC SA02110CH](https://openairdocs.org/stc/SA02110CH): Installation of a Time Trac Data Recorder. P2 Incorporated - [STC SA2693NM](https://openairdocs.org/stc/SA2693NM): Installation of Electronics International digital volt/amp gauges and accessories. Electronics International Inc - [STC SA4005NM](https://openairdocs.org/stc/SA4005NM): Precise Flight Inc. Pulselite Control System. Precise Flight Inc - [STC SA00961CH](https://openairdocs.org/stc/SA00961CH): Installation of hydraulically driven material dispersal gate for fire fighting applications. Turbine Conversions Ltd - [STC SA00171BO](https://openairdocs.org/stc/SA00171BO): Installation of Pratt & Whitney Engine Services, Inc. Aircraft Data Acquisition System ADAS+, P/N ADAS-K-010. Pratt & Whitney Engine Services Inc - [STC SA04677CH](https://openairdocs.org/stc/SA04677CH): Installation of a Powered Hopper Lid and Auger System. Reabe Design LLC - [STC SA01639NY](https://openairdocs.org/stc/SA01639NY): Replacement of 12 refrigerant in air conditioning system with Enviro Refrigerant Hotshot R414B. Scale Modelbuilders Inc All 67: https://openairdocs.org/aircraft/N107ML/stcs.md ## Related - Other Air Tractor AT-402B aircraft: https://openairdocs.org/model/air-tractor-at-402b/aircraft.md - The Pratt & Whitney Canada PT6A-34AG engine: https://openairdocs.org/engine/pratt-whitney-canada-pt6a-34ag.md --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.