Bringing an external GPS device on a plane might not be the smartest thing these days. Have fun explaining that to the air marshall.
EDIT: Beat me to the list!
A bit off topic, but here is the latest list I could find online of airlines that allow the use of GPS by passengers enroute.
Note: These are reports from newsgroup users.
Revised August 2010
Please let me know of any errors or additions. Joe Mehaffey
The Airlines which OFFICIALLY APPROVE the use of GPS receivers during CRUISE.
Aer Lingus
Air Canada
Air China
Air France
Air New Zealand
Air Malaysia
Air Tanzania
Alitalia (Italy)
Braathens (owned by SAS) Norway
British Airways
Cathay Pacific
CAAC (China Airlines, Mainland China)
China Southern Airlines
Continental Airlines (as of August 2007, changed AGAIN! 4th time!)
CrossAir
Delta Airlines (as of May 2009, UNteathered HANDHELD GPS units only allowed.)
DragonAir (China)
EasyJet (Europe)
Egypt Air
FinnAir
FlyBe Airlines (UK)
Icelandair
Jet Airways (India)
JetBlue Airways (USA, Changed back to OK as of April 2007)
KLM (Flight operations book under rule 120.8.5)
LAN Airlines Argentina
LOT Polish Airlines
Maersk Air (Denmark)
MidWest Express (USA)
Nationwide Airlines (South Africa)
NorthWest Airlines (Flight operations book under rule 120.8.5)
Precision Air (Tanzania)
Olympic Airlines (Greece)
Qantas as of 3/2/2007 per Tania<websupport@qantas.com.au> (yep.. Changed AGAIN!)
Singapore Air Lines
SAS
SN Brussels Airlines (as of 11/25/03 per <KTeirbroodt@brusselsairlines.com>
South African Airways
SouthWest Airlines (Changed AGAIN as of January 2009.. This is THREE changes in since early 2008.)
Sun Country (Regional USA)
Swiss (Was Swissair and CrossAir)
Tunis Air
United Air Lines (may ask if your GPS is FCC Class B approved. All handhelds are. Show them in the manual.)
Vanguard Airlines
WestJet Airlines (Canada)
Airlines which OFFICIALLY DO NOT APPROVE the use of GPS receivers at ANY time during flight.
(*) Individual Pilots may allow GPS use.
Alaska Airlines
Air Tran
America West Airlines
American Airlines (Changed again as of October 2009)
Britannia Airlines
El Al Airlines (Israel)
Frontier Airlines (as of June 2008)
Hawaiian Airlines(*)
Horizon Airlines(*)
Iberia Airlines(*)
Lufthansa Airlines
Mexicana airlines
Midway Express
Monarch Airlines
Ryanair (Irish) (as of January 2008)
Spirit Airlines
US Airways (was US Air) (as of December 2007)
Varig Airlines
Virgin Airlines (As of March 2007)