References:

Wikipedia:

http://en.wikipedia.org/wiki/Lockheed_L-188_Electra
http://en.wikipedia.org/wiki/Allison_T56
http://en.wikipedia.org/wiki/Northwest_Orient_Airlines_Flight_710
http://en.wikipedia.org/wiki/Northwest_Orient_Airlines

Information about the Cannelton Crash:
http://www.courier-journal.com/apps/pbcs.dll/article?AID=20102210304
http://aviation-safety.net/database/record.php?id=19600317-0
http://maps.google.com/maps?ll=37.911006,-86.633008
http://crankyflier.com/2008/11/17/memorial-for-northwest-flight-710/comment-page-1
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=11122
http://www.waymarking.com/waymarks/WM63FJ_ELECTRA_AIR_CRASH_SITE_MEMORIAL_MILLSTONE_INDIANA

Information about the Electra Design Defect:
http://www.airspacemag.com/military-aviation/The_Hammer.html
http://www.ijme.us/cd_06/PDF/ENG%20204-005.pdf
http://www.cs.clemson.edu/~steve/Spiro/electra1.html
http://www.cs.clemson.edu/~steve/Spiro/electra2.html
http://www.airliners.net/aviation-forums/general_aviation/read.main/279117/
http://www.epi-eng.com/aircraft_engine_conversions/whirl_mode.htm
http://www.adastron.com/lockheed/electra/leap.htm

Official Lockheed page on the L188 Electra:
http://www.lockheedmartin.com/ams/L188Electra.html

Additional information on the L188 Electra & P3 Orion:
http://www.prop-liners.com/l188tech.htm
http://www.airliners.net/aircraft-data/stats.main?id=268
http://www.stinsonflyer.com/prop/l188-2.jpg

http://www.aviastar.org/air/usa/lok_l-188.php
http://www.globalsecurity.org/military/systems/aircraft/p-3-history.htm

Desktop model of a Northwest Electra:
http://store.tailwinds.com/northwest-l-188-electra-model-planes.html

Additional information on the Allison 501-D (T56):
http://www.nasm.si.edu/collections/artifact.cfm?id=A19620071000
http://www.rolls-royce.com/defence/products/transporters/t56.jsp

Other relevant links:

"Northwest Airlines: The First Eighty Years" , by Geoff Jones (page 52):
http://books.google.com/books?id=y0ERUPZ1TrQC&dq=Northwest+orient+schedule,+1960&source=gbs_navlinks_s

NORTHWEST AIRLINES, INC.: An Inventory of Its Corporate Records at the Minnesota Historical Society:
http://www.mnhs.org/library/findaids/00110.xml

March 17, 2009 Emergency Management Higher Education Program Notes:
http://training.fema.gov/EMIWeb/edu/ARRPT/March%2017,%202009.doc

Additional references used:

1. "Airpower" magazine May 2003. "Electra!" 

2. "Tell City News" page 1, 2, 7, 8 - March 25, 1960

3. "Air Disaster, Volume 4", by Macarthur Job. Chapter 13,"The Lockheed Electra Saga"