# Continental TSIO-520-T

- Type: Engine model (FAA registry)
- Registry code: 17269
- Manufacturer (registry): CONT MOTOR
- Model: TSIO-520-T
- Engine type: Reciprocating
- Power: 310 hp
- Data sheet: [TCDS E8CE](https://openairdocs.org/tcds/E8CE) (OpenAirDocs)
- Holder: Continental Aerospace Technologies, Inc.
- Installed in: 1 registered aircraft
- Page: https://openairdocs.org/engine/continental-tsio-520-t

Model codes come from the FAA registry's reference file.

## ADs that may apply (OpenAirDocs)

Matched to this engine model by model name and maker. Each AD's applicability may narrow it by serial number, part number or equipment.

- [AD 2023-17-04](https://openairdocs.org/ad/2023-17-04): Reciprocating Engine Oil System · F & M Enterprises' Model C6LC, C6LC-S or C6LC-L oil filter… (Stratus Tool Technologies STC SE09356SC or 2 others). Effective Oct 26, 2023
- [AD 2023-09-09](https://openairdocs.org/ad/2023-09-09): Exhaust Turbine System (Recip) · Aerostar PA-60-600 (Aerostar 600), PA-60-601 (Aerostar 601), PA-60-601P (Aerostar 601P) and 292 more. Effective Jul 17, 2023
- [AD 2023-05-16](https://openairdocs.org/ad/2023-05-16): Reciprocating Engine Power Section · Continental Aerospace Technologies GTSIO-520-C, GTSIO-520-D, GTSIO-520-H and 147 more. Effective Mar 15, 2023
- [AD 2023-02-12](https://openairdocs.org/ad/2023-02-12): Engine Air Intake System · Continental Aerospace Technologies GTSIO-520-C, GTSIO-520-D, GTSIO-520-E and 127 more. Effective Feb 17, 2023
- [AD 2022-16-03](https://openairdocs.org/ad/2022-16-03): Engine (RECIPROCATING) · Continental Aerospace Technologies GTSIO-520-C, GTSIO-520-D, GTSIO-520-F and 236 more. Effective Aug 15, 2022
- [AD 2016-16-12](https://openairdocs.org/ad/2016-16-12): Cylinder assemblies · Continental Motors LTSIO-520-AE, TSIO-520-A, TSIO-520-AE and 89 more. Effective Sep 15, 2016
- [AD 2014-05-29](https://openairdocs.org/ad/2014-05-29): SAP replacement parts manufacturer approval (PMA) investment cast cylinder assemblies · Continental Motors TSIO-520-A, TSIO-520-AE, TSIO-520-AF and 55 more. Effective Apr 25, 2014
- [AD 2012-03-06](https://openairdocs.org/ad/2012-03-06): Fuel servo diaphragm · Continental Motors 6-260-A, 6-285-A, 6-285-B and 482 more. Effective Feb 24, 2012
- [AD 2011-13-03](https://openairdocs.org/ad/2011-13-03): Turbocharger Turbine · Lycoming Engines LTO-360-E1A6D, O-540-L3C5D, TIGO-541-E1A and 20 more. Effective Jul 13, 2011
- [AD 2010-11-04](https://openairdocs.org/ad/2010-11-04): Hydraulic lifters · Continental Motors FSO-470-A, GIO-470-A, GTSIO-520-C and 190 more. Effective Jun 16, 2010
- [AD 2010-07-08](https://openairdocs.org/ad/2010-07-08): Turbochargers · Kelly Aerospace Energy Systems HIO-360-E1AD, HIO-360-E1BD, HIO-360-F1AD and 137 more. Effective Apr 19, 2010
- [AD 2009-19-07](https://openairdocs.org/ad/2009-19-07): EQ3 cylinders · Continental Motors IO-470-C, IO-470-D, IO-470-E and 72 more. Effective Oct 7, 2009
- [AD 2007-04-19 R1](https://openairdocs.org/ad/2007-04-19-R1): SAP cylinder assemblies · Lycoming Engines AEIO-320-D1B, AEIO-320-D2B, AEIO-320-E1A and 314 more. Effective May 7, 2007
- [AD 2004-08-10](https://openairdocs.org/ad/2004-08-10): Serial-numbered (SN) cylinders · Modify Teledyne Continental TSIO-520-NB engine (RAM Aircraft Limited Partnership STC SE09104SC or 4 others). Effective May 5, 2004
- [AD 2000-23-21](https://openairdocs.org/ad/2000-23-21): Crankshaft · Continental Motors IO-360-A, IO-360-AB, IO-360-B and 164 more. Effective Dec 12, 2000
- [AD 99-19-01](https://openairdocs.org/ad/99-19-01): No. 2 and No. 5 Crankshaft Inspections · Continental Motors GTSIO-520-C, GTSIO-520-D, GTSIO-520-E and 127 more. Effective Sep 30, 1999
- [AD 97-26-17](https://openairdocs.org/ad/97-26-17): Crankshaft · Continental Motors IO-360-A, IO-360-AB, IO-360-B and 90 more. Effective Jan 23, 1998
- [AD 96-12-22](https://openairdocs.org/ad/96-12-22): Full Flow Engine Oil Adapter · Bellanca CH-300 Pacemaker, 120, 140 and 361 more. Effective Jul 31, 1996
- [AD 93-08-17](https://openairdocs.org/ad/93-08-17): Oil Pick-Up Tube · Continental Motors IO-470-A, IO-470-C, IO-470-D and 104 more. Effective Aug 23, 1993
- [AD 93-10-02](https://openairdocs.org/ad/93-10-02): Missing Cylinder Valve Retainer Key · Continental Motors GTSIO-520-C, GTSIO-520-D, GTSIO-520-E and 180 more. Effective Aug 12, 1993
- [AD 91-19-03](https://openairdocs.org/ad/91-19-03): Oil Filter · Continental Motors 6-285-A, 6-285-B, 6-285-BA and 169 more. Effective Sep 29, 1991
- [AD 88-03-06](https://openairdocs.org/ad/88-03-06): Oil Filter · Continental Motors GTSIO-520-C, GTSIO-520-D, GTSIO-520-E and 155 more. Effective Apr 15, 1988
- [AD 86-13-04 R3](https://openairdocs.org/ad/86-13-04-R3): Cylinder Assemblies · Continental Motors GTSIO-520-C, GTSIO-520-D, GTSIO-520-H and 44 more. Effective Feb 24, 1988
- [AD 81-24-06](https://openairdocs.org/ad/81-24-06): Engine Driven Fuel Pumps · Continental Motors GTSIO-520-C, GTSIO-520-D, GTSIO-520-E and 51 more. Effective Nov 23, 1981
- [AD 81-16-05](https://openairdocs.org/ad/81-16-05): Magnetos · Lycoming Engines AEIO-320-E1B, AEIO-320-E2B, AEIO-360-B1G6 and 234 more. Effective Aug 6, 1981
- [AD 80-06-05](https://openairdocs.org/ad/80-06-05): Magnetos · Lycoming Engines AEIO-320-D1B, AEIO-320-D2B, AEIO-320-E1A and 254 more. Effective Mar 28, 1980
- [AD 80-01-04](https://openairdocs.org/ad/80-01-04): Cylinder Holddown Flange Assemblies · Continental Motors IO-520-A, IO-520-B, IO-520-BA and 44 more. Effective Jan 25, 1980
- [AD 79-05-09](https://openairdocs.org/ad/79-05-09): Oil Pump Assembly Or Oil Pressure Relief Valve Screw And/Or Plunger · Teledyne Continental Motors 6-285-CA, GTSIO-520-C, GTSIO-520-D and 60 more. Effective Mar 12, 1979
- [AD 98-01-08](https://openairdocs.org/ad/98-01-08): Exhaust Roller Rocker Arm · Roller rocker arm P/N PE 92I intake and PE92E exhaust (Performance Engineering STC SE8594SW)

Historical (superseded or no longer in force):

- [AD 2023-04-08](https://openairdocs.org/ad/2023-04-08) (historical): Reciprocating Engine Power Section · Continental Aerospace Technologies GTSIO-520-C, GTSIO-520-D, GTSIO-520-H and 141 more. Effective Feb 23, 2023
- [AD 2009-24-52](https://openairdocs.org/ad/2009-24-52) (historical): Hydraulic lifters · Continental Motors FSO-470-A, GIO-470-A, GTSIO-520-C and 192 more
- [AD 2009-24-51](https://openairdocs.org/ad/2009-24-51) (historical): Hydraulic lifters · Teledyne Continental Motors FSO-470-A, GIO-470-A, GTSIO-520-C and 156 more
- [AD 2009-16-03](https://openairdocs.org/ad/2009-16-03) (historical): Cylinder assemblies · Continental Motors IO-520-A, IO-520-B, IO-520-BA and 55 more. Effective Sep 9, 2009
- [AD 2000-08-51](https://openairdocs.org/ad/2000-08-51) (historical): Crankshaft · Teledyne Continental Motors IO-360-A, IO-360-AB, IO-360-B and 158 more
- [AD 99-09-17](https://openairdocs.org/ad/99-09-17) (historical): Crankshaft · Teledyne Continental Motors IO-470-A, IO-470-C, IO-470-D and 114 more

## Information bulletins (advisory) (10)

- [SAIB NE-20-05](https://openairdocs.org/saib/NE-20-05): POWERPLANT - Engine Camshaft Gear Tooth Fracture. Issued Apr 6, 2020
- [SAIB NE-18-16](https://openairdocs.org/saib/NE-18-16): POWERPLANT  Alternator Drive Coupling. Issued Jun 20, 2018
- [SAIB NE-17-11](https://openairdocs.org/saib/NE-17-11): POWERPLANT  Engine damage as a result of kickback. Issued May 10, 2017
- [SAIB NE-16-13](https://openairdocs.org/saib/NE-16-13): Powerplant - Prohibited use of sealant. Issued Mar 8, 2016
- [SAIB NE-13-15](https://openairdocs.org/saib/NE-13-15): Engine Controls: Continental Motors, Inc. (CMI) Throttle and Mixture Control Levers. Issued Feb 8, 2013
- [SAIB NE-13-04](https://openairdocs.org/saib/NE-13-04): Continental Motors, Inc. (CMI) Connecting Rod Piston Pin Bushing Inspection. Issued Oct 31, 2012
- [SAIB NE-10-09](https://openairdocs.org/saib/NE-10-09): Reciprocating Engine Power Section: Hydraulic Valve Lifters. Issued Nov 20, 2009
- [SAIB NE-10-07](https://openairdocs.org/saib/NE-10-07): Reciprocating Engine Cylinder: Identification Information for Superior Air Parts, PMA Cylinder Heads for Teledyne Continental Motors (TCM) IO-520, TSIO-520,and IO-550 Series Engines.. Issued Nov 2, 2009
- [SAIB NE-09-08](https://openairdocs.org/saib/NE-09-08): Reciprocating Engine Cylinder Section. Issued Jan 30, 2009
- [SAIB NE-07-09R1](https://openairdocs.org/saib/NE-07-09R1): Periodic Inspections of ECi Cylinder Assemblies for Cracks in the Aluminum Head. Issued Mar 21, 2007

## Registered aircraft (1)

- [N385SP](https://openairdocs.org/aircraft/N385SP): [Aircraft Trustee Services Inc Trustee](https://openairdocs.org/faa-owner/AIRCRAFT%20TRUSTEE%20SERVICES%20INC%20TRUSTEE), [Dover, DE](https://openairdocs.org/faa-place/DE/Dover), built 1979, S/N T18803452T

## 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 CEN14LA480](https://openairdocs.org/ntsb/CEN14LA480), Aug 16, 2014: Cessna 188 (N878C), Hearne, TX, substantial damage. Probable cause: The pilot’s failure to maintain clearance from a crop.

## 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 20140816012849A](https://openairdocs.org/incident/20140816012849A), Aug 16, 2014: Cessna T188C (N878C), Hearne, TX, Destroyed. Aircraft was on a spray run and contacted crop. Heavy friction with milo heads decelerated the aircraft as it struck a six strand barbed wire fence and metal…

## Service difficulty reports (9)

As reported by operators and repair stations, by the model named in the report.

- [SDR 2013FA0000161](https://openairdocs.org/sdr/2013FA0000161), Mar 11, 2013: SKIN. DAMAGED. PERFORMED A POST PAINT STRIP INSPECTION AND FOUND A VERY LARGE QTY OF UNIVERSAL HEAD RIVETS HAD BEEN SANDED DOWN.
- [SDR 2009FA0000601](https://openairdocs.org/sdr/2009FA0000601), May 31, 2009: BRACKET. FATIGUED. LANDING GEAR BRACKET ASSY FAILED ON TAKEOFF DUE TO METAL FATIGUE, CAUSING ABORTED TAKEOFF, SUBSTANTIAL DAMAGE TO THE ACFT. DATA DERIVED FROM FAA FORM 8020-23 DA
- [SDR FTW04LA214](https://openairdocs.org/sdr/FTW04LA214), Aug 16, 2004: SWITCH. DEFECTIVE. AIRCRAFT LOST POWER ON LANDING. CRASHED SHORT OF FIELD. DETERMINED (HI-SIDE) OF EMERGENCY FUEL PUMP SWITCH STUCK IN THE HI POSITION.
- [SDR 2004FA0000675](https://openairdocs.org/sdr/2004FA0000675), Jul 20, 2004: CRANKSHAFT. BROKEN. TSIO-520-T CRANKSHAFT BROKE AT 1776 HOURS SINCE FACTORY REMANUFACTURE. OPERATED BEYOND RECOMMENDED OVERHAUL, CRANK FAILED CAUSING UNSCHEDULED LANDING THAT RESUL
- [SDR CA030220008](https://openairdocs.org/sdr/CA030220008), Feb 20, 2003: CONTROL CABLE. FRAYED. (CAN) AILERON DIRECT CABLE FRAYED AT NYLON PULLEYS IN CABIN ROOF AREA
- [SDR 2003FA0000088](https://openairdocs.org/sdr/2003FA0000088), Jan 14, 2003: INTAKE VALVE. LEAKING. AT 470 HOURS ON REBUILT ENGINE, ALL CYLINDERS WERE REMOVE FOR INTAKE VALVE LEAKAGE. ALL VALVE SEATS WERE EASILY RECONDITIONED, BUT VALVES SHOWED MAJOR IDENTATIO
- [SDR 96ZZZX5483](https://openairdocs.org/sdr/96ZZZX5483), Oct 22, 1996: HOSE. LEAKING. THE ENGINE LOST POWER, AN EMERGENCY LANDING ACCOMPLISHED WITH SMOKE COMING FROM THE ENGINE. AN EXAMINATION OF THE ENGINE FOUND THE FUEL HOSE BETWEEN THE THROTTL
- [SDR 95ZZZX3987](https://openairdocs.org/sdr/95ZZZX3987), Jul 23, 1995: CRANKSHAFT. BROKE. NEW V.A.R. CRANKSHAFT BROKE BETWEEN NR 2 AND NR 3 CYLINDERS. THIS CRANKSHAFT HAD A TOTAL TIME OF 442 HOURS SINCE NEW. FAILURE WAS IN-FLIGHT AND PILOT MADE SAFE 
- [SDR 95ZZZX831](https://openairdocs.org/sdr/95ZZZX831), Jan 1, 1995: CRANKSHAFT. HIGH RUNOUT. ENGINE WAS DISASSEMBLED FOR REPAIR OF CRACKED CRANKCASE. INSPECTION OF CRANKSHAFT 631716 REVEALED HIGH RUN-OUT OF ALL MEASUREMENT POINTS, BUT NO CRACKS. ENGINE 

## STCs that may be installed (OpenAirDocs) (45)

Approved for this engine model: the STC's model list names it on its data sheet, or a series that includes it. In force first, then newest. The registry doesn't record which STCs an aircraft has.

- [STC SE5583SW](https://openairdocs.org/stc/SE5583SW): Installation of fuel flow transducers (true-flow totalizer). Alcor LLC. Lists TSIO-520 Series
- [STC SE04349CH](https://openairdocs.org/stc/SE04349CH): Installation of SureFly electronic ignition. SureFly Partners Ltd
- [STC SE02352CH](https://openairdocs.org/stc/SE02352CH): Installation of Challenger cleanable oil filter assembly. Challenger Aviation Products Inc
- [STC SE03309CH](https://openairdocs.org/stc/SE03309CH): Installation of Engine Preheat Kit, p/n TSP6CYL-2927-115 for 115 volt application. Hartzell Propeller Inc
- [STC SE04577CH](https://openairdocs.org/stc/SE04577CH): Install an electronic engine ignition system. Electroair Acquisition Corp
- [STC SE09356SC](https://openairdocs.org/stc/SE09356SC): Install F & M Enterprises' Model C6LC, C6LC-S or C6LC-L oil filter adapter for a spin-on oil filter. Stratus Tool Technologies LLC
- [STC SE00113SE](https://openairdocs.org/stc/SE00113SE): Replaces Teledyne-Continental Part Number 646277 lifter bodies. B & B Aviation LLC
- [STC SE5784NM](https://openairdocs.org/stc/SE5784NM): Replacement of Teledyne Continental original camshaft. B & B Aviation LLC
- [STC SE70RM](https://openairdocs.org/stc/SE70RM): Installation of compressor bracket. Air Comm Corporation
- [STC SE09637SC](https://openairdocs.org/stc/SE09637SC): Remove existing rocker arm assemblies and install modify rocker arm assemblies. General Aviation Modifications Inc
- [STC SE1462CE](https://openairdocs.org/stc/SE1462CE): Installation of SSP Products P/N 3208672-91 heater core and P/N 3208677-104 shroud. Textron Aviation Inc
- [STC SE1186SW](https://openairdocs.org/stc/SE1186SW): Regrooving of pistons P/N 631475 or P/N 632585. Continental Motors, Inc
- [STC SE5820SW](https://openairdocs.org/stc/SE5820SW): Installation of Airmotive exhaust valve, P/N AEC-637781. Continental Motors, Inc. Lists TSIO-520 Series
- [STC SE8776SW](https://openairdocs.org/stc/SE8776SW): Installation of coated cylinders and piston rings. Continental Motors, Inc. Lists TSIO-520 Series
- [STC SE3330NM](https://openairdocs.org/stc/SE3330NM): Continental valve cover gasket. Real Gaskets Tennessee
- [STC SE09280SC-D](https://openairdocs.org/stc/SE09280SC-D): Modify engine in accordance with RAM Aircraft Corporation Drawing No. 1888. RAM Aircraft Limited Partnership
- [STC SE3631SW-D](https://openairdocs.org/stc/SE3631SW-D): Cylinder modifications. RAM Aircraft Limited Partnership
- [STC SE09846SC](https://openairdocs.org/stc/SE09846SC): Installation of S539800M30 starter adapter springs. Aircraft Specialties Services Inc
- [STC SE630SW](https://openairdocs.org/stc/SE630SW): Engine modifications. RAM Aircraft Limited Partnership
- [STC SE1780NM](https://openairdocs.org/stc/SE1780NM): Installation of Precise Flight standby vacuum system (SVS III). Precise Flight Inc
- [STC SE00521DE](https://openairdocs.org/stc/SE00521DE): Limited to installation on model TSIO-520-T, serial number 515040 only. Buckspan Ken
- [STC SE5743NM](https://openairdocs.org/stc/SE5743NM): Intallation of adapter for externally mounted oil filter. Aviation Development Corporation
- [STC SE09261SC](https://openairdocs.org/stc/SE09261SC): Modify engine to increase power output rating from 310 hp to 335 hp, install Garrett/AlliedSignal TA-81 turbocharger, RAM intercooler, RAM economy camshaft, RAM oil pump pickup tube, RAM forged pistons with gapless rings, and 0.02 inch undersized crankshaft. RAM Aircraft Limited Partnership. Lists TSIO-520 Series
- [STC SE3631SW](https://openairdocs.org/stc/SE3631SW): Cylinder modification. RAM Aircraft Limited Partnership. Lists TSIO-520 Series
- [STC SE09513SC](https://openairdocs.org/stc/SE09513SC): Installation and usage of Exxon 20W50 Multigrade aircraft engine oil conforming to Exxon Oil Formulation WS-3013. Exxon Company USA. Lists TSIO-520 Series
- [STC SE09559SC](https://openairdocs.org/stc/SE09559SC): Installation of US Airparts roller rocker arm assemblies P/N US92E exhaust and US92I intake. US Airparts, Inc
- [STC SE55WE](https://openairdocs.org/stc/SE55WE): Modification of fuel injection manifold valve P/N 626547 to the P/N 631427 or P/N 636326 configuration. AAR Aircraft Services Inc. d/b/a AAR Aircraft Services-Oklahoma. Lists TSIO-520 Series
- [STC SE09289SC](https://openairdocs.org/stc/SE09289SC): Installation of modified fuel injector nozzles. General Aviation Modifications, Inc. Lists TSIO-520 Series
- [STC SE09319SC](https://openairdocs.org/stc/SE09319SC): Modify oil pan adding a new oil sump drain. Texas Skyways Inc. Lists TSIO-520 Series
- [STC SE00350SE](https://openairdocs.org/stc/SE00350SE): Installation of sump mounted chip detector. Aviation Development Corporation
- [STC SE00144SE](https://openairdocs.org/stc/SE00144SE): Replaces the following Teledyne-Continental part numbers: 641682 (Rocker Arm, Exhaust), 539742 (Rocker Arm, Intake), 539740 (Rocker Arm, Shaft) and 538304 (Pushrod Assembly). Dakota Aircraft Parts Inc
- [STC SE8687SW](https://openairdocs.org/stc/SE8687SW): Regrooving of pistons P/N 631475 or P/N 632585. Capehart Industries, Inc. Lists TSIO-520 Series
- [STC SE00005DE](https://openairdocs.org/stc/SE00005DE): Installation of engine oil filter adapter compatable with SA4094NM Oilamatic, Inc. engine preoiling system. Oilamatic Inc
- [STC SE8594SW](https://openairdocs.org/stc/SE8594SW): Installation of roller rocker arm P/N PE 92I intake and PE92E exhaust. Performance Engineering
- [STC SE2115CE](https://openairdocs.org/stc/SE2115CE): Replacement of exhaust and intake system, installation of intercooler, modification of engine oil pump and scavenge oil pump, and replacement of turbocharger control with an oil regulated system. Air Plains Services Corporation
- [STC SE5205NM](https://openairdocs.org/stc/SE5205NM): Installation of an Oilamatic engine filter screen adapter. Oilamatic Inc
- [STC SE7430SW](https://openairdocs.org/stc/SE7430SW): Installation of Performance Engineering roller rocker arms. Performance Engineering
- [STC SE941GL](https://openairdocs.org/stc/SE941GL): Installation of oil filler tube extension. Rapco, Inc
- [STC SE452NE](https://openairdocs.org/stc/SE452NE): Installation and usage of 'Mobil AV 1' aviation oil. Mobil Research & Development Corp. Lists TSIO-520 Series
- [STC SE3630SW](https://openairdocs.org/stc/SE3630SW): Crankcase modifications. RAM Aircraft Limited Partnership
- [STC SE5879SW](https://openairdocs.org/stc/SE5879SW): Use of Phillips X/C II 20W-50 and25W-60 oil (OSS 55875) in all Avco reciprocating aircraft engines from 65 to 450 BHP. Phillips Petroleum Co. Lists TSIO-520 Series
- [STC SE244NE](https://openairdocs.org/stc/SE244NE): Installation of Mattituck plasma flame sprayed cylinder barrels in Teledyne reciprocating engines. Mattituck Airbase, Inc. Lists TSIO-520 Series
- [STC SE80NE](https://openairdocs.org/stc/SE80NE): Installation and usage of Bel-Ray synthetic aviation oil, Bel-Ray Aero 1, (nonsupercharged), horizontally opposed direct drive, aircraft engines of 350 hp. or less. Bel-Ray Company, Inc. Lists TSIO-520 Series
- [STC SE44WE](https://openairdocs.org/stc/SE44WE): Use of Kling Aviation Oil, Specifications KL-100, KL-200 and KL-300 in Continental and Lycoming engines. Kling Oil Company. Lists TSIO-520 Series
- [STC SE09280SC](https://openairdocs.org/stc/SE09280SC) (historical): Modify engine in accordance with RAM Aircraft Corporation Drawing No. 1888. RAM Aircraft Limited Partnership

---
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.
