Why do the Alaska and the Hawaii airport codes begin with “P” whereas airports in the lower 48 begin with “K” 
When I choose to view a flight using the view airport feature at an airport assigned a “P” code and the flight is flying to another airport also assigned a “P” code "the hyperlink shows the airport to be a “K” airport
The “P” stands for “Pacific”.
Now why they decided to distinguish that is a mystery to me.
Isaac
It all has to do with the ICAO region that the airports are located in. The first letter usually indicates the region and the 2nd letter indicates the country. In these cases, the rest of the code is the 3 letter IATA/FAA code. In most cases, when it is a single letter identifier the rest of the code is is the IATA/FAA code such as KJFK or CYYZ. However, I noticed that China has a single letter (“Z”) but the code is not simply “Z” followed by the 3 letter code.
The USA isn’t alone in having more than 1 region code. Hong Kong has “VH” and Macao uses “VM” while the rest of China uses “Z”. Kirabati, an island nation in the Pacific, uses 2 codes. It appears that these two countries have different ICAO codes because they are merged nations (i.e. Hong Kong and Macao went to China and Kairabati is composed of two different colonies that were merged to form a single country). The USA appears to be alone in always having more than one ICAO code.
Here’s a list of the codes from answer.com
AG = Solomon Islands
AN = Nauru
AY = Papua New Guinea
BG = Greenland
BI = Iceland
C = Canada
DA = Algeria
DB = Benin
DF = Burkina Faso
DG = Ghana
DI = Cte d’Ivoire
DN = Nigeria
DR = Niger
DT = Tunisia
DX = Togolese Republic
EB = Belgium
ED = Germany (Civil)
EE = Estonia
EF = Finland
EG = United Kingdom of Great Britain and Northern Ireland
EH = Netherlands
EI = Ireland
EK = Denmark
EL = Luxembourg
EN = Norway
EP = Poland
ES = Sweden
ET = Germany (Military)
EV = Latvia
EY = Lithuania
FA = South Africa
FB = Botswana
FC = Republic of the Congo
FD = Swaziland
FE = Central African Republic
FG = Equatorial Guinea
FH = Ascension Island
FI = Mauritius
FJ = British Indian Ocean Territory
FK = Cameroon
FL = Zambia
FM = Comoros, Madagascar, Mayotte, Runion
FN = Angola
FO = Gabon
FP = So Tom and Prncipe
FQ = Mozambique
FS = Seychelles
FT = Chad
FV = Zimbabwe
FW = Malawi
FX = Lesotho
FY = Namibia
FZ = Democratic Republic of the Congo
GA = Mali
GB = The Gambia
GC = Canary Islands (Spain)
GF = Sierra Leone
GG = Guinea-Bissau
GL = Liberia
GM = Morocco
GO = Senegal
GQ = Mauritania
GS = Western Sahara
GU = Guinea
GV = Cape Verde
HA = Ethiopia
HB = Burundi
HC = Somalia
HD = Djibouti (also HF)
HE = Egypt
HH = Eritrea
HK = Kenya
HL = Libya
HR = Rwanda
HS = Sudan
HT = Tanzania
HU = Uganda
K = United States of America (Continental)
LA = Albania
LB = Bulgaria
LC = Cyprus
LD = Croatia
LE = Spain
LF = France
LG = Greece
LH = Hungary
LI = Italy
LJ = Slovenia
LK = Czech Republic
LL = Israel
LM = Malta
LN = Monaco
LO = Austria
LP = Portugal (includes Azores)
LQ = Bosnia and Herzegovina
LR = Romania
LS = Switzerland
LT = Turkey
LU = Moldova
LV = Gaza Strip
LW = Macedonia
LX = Gibraltar
LY = Serbia and Montenegro
LZ = Slovakia
MB = Turks and Caicos Islands
MD = Dominican Republic
MG = Guatemala
MH = Honduras
MK = Jamaica
MM = Mexico
MN = Nicaragua
MP = Panama
MR = Costa Rica
MS = El Salvador
MT = Haiti
MU = Cuba
MW = Cayman Islands
MY = Bahamas
MZ = Belize
NC = Cook Islands
NF = Fiji, Tonga
NG = Kiribati (Gilbert Islands), Tuvalu
NI = Niue
NL = Wallis and Futuna
NS = Samoa
NT = French Polynesia
NV = Vanuatu
NW = New Caledonia
NZ = New Zealand
OA = Afghanistan
OB = Bahrain
OE = Saudi Arabia
OI = Iran
OJ = Jordan and the West Bank
OK = Kuwait
OL = Lebanon
OM = United Arab Emirates
OO = Oman
OP = Pakistan
OR = Iraq
OS = Syria
OT = Qatar
OY = Yemen
PA = United States of America (Alaska)
PB = Baker Island
PC = Kiribati (Phoenix Islands)
PG = Guam, Northern Marianas
PH = United States of America (Hawaii)
PJ = Johnston Atoll
PK = Marshall Islands
PL = Kiribati (Line Islands)
PM = Midway Island
PT = Federated States of Micronesia, Palau
PW = Wake Island
RC = Taiwan
RJ = Japan (most of country)
RK = South Korea
RO = Japan (Okinawa Prefecture and Yoron)
RP = Philippines
SA = Argentina
SB = Brazil
SC = Chile
SE = Ecuador
SF = Falkland Islands
SG = Paraguay
SK = Colombia
SL = Bolivia
SM = Suriname
SO = French Guiana
SP = Peru
SU = Uruguay
SV = Venezuela
SY = Guyana
TA = Antigua and Barbuda
TB = Barbados
TD = Dominica
TF = Guadeloupe
TG = Grenada
TI = U.S. Virgin Islands
TJ = Puerto Rico
TK = Saint Kitts and Nevis
TL = Saint Lucia
TN = Netherlands Antilles, Aruba
TQ = Anguilla
TR = Montserrat
TT = Trinidad and Tobago
TU = British Virgin Islands
TV = Saint Vincent and the Grenadines
TX = Bermuda
U = Russia (except UA, UB, UG, UK, UM and UT)
UA = Kazakhstan, Kyrgyzstan
UB = Azerbaijan
UG = Armenia, Georgia
UK = Ukraine
UM = Belarus
UT = Tajikistan, Turkmenistan, Uzbekistan
VA = India (also VE, VI and VO)
VC = Sri Lanka
VD = Cambodia
VG = Bangladesh
VH = Hong Kong
VL = Laos
VM = Macao
VN = Nepal
VQ = Bhutan
VR = Maldives
VT = Thailand
VV = Vietnam
VY = Myanmar
WA = Indonesia (also WI, WQ, WR)
WB = Malaysia (also WM), Brunei
WP = Timor-Leste
WS = Singapore
Y = Australia
Z = People’s Republic of China (except ZK and ZM)
ZK = North Korea
ZM = Mongolia
To add to the confusion, some airfields have 2 ICAO codes- PHNL is also PHIK for Hickam AFB. They share the runways but are the civil and military sides.
Ther are also a few “K” airfields in Europe too. All Air Force Bases. I forget the codes off the top of my head, but there are a few METAR stations that are “K” and airfield associated. There area also a few “E” codes in Germany (old West Germany) such as Ramstein AFB.
All Germany’s airfields are ‘E…’ 
Sorry I meant to say “ET” instead of “ED”