Pilot David Knadler has visited (landed in) a total of 54 countries but have 186 countries yet to explore.
Azerbaijan
Bahamas, The
Bahrain
Barbados
Belgium
Benin
Bermuda
Bosnia and Herzegovina
Botswana
Brazil
British Indian Ocean Territory
British Virgin Islands
Brunei
Bulgaria
Burkina Faso
Burundi
Cambodia
Cameroon
Cape Verde
Cayman Islands
Central African Republic
Chad
China
Christmas Island
Cocos (Keeling) Islands
Colombia
Comoros
Congo
Cook Islands
Cote D'Ivoire
Cuba
Cyprus
Czech Republic
Denmark
Djibouti
Dominica
Dominican Republic
Ecuador
Egypt
El Salvador
Equatorial Guinea
Eritrea
Eswatini
Ethiopia
Faroe Islands
Fiji
French Guiana
French Polynesia
Gabon
Gambia
Georgia
Germany
Ghana
Guinea
Guinea-Bissau
Guyana
Haiti
Honduras
Hong Kong
Iceland
Jamaica
Jersey
Johnston Atoll
Jordan
Kazakhstan
Kenya
Kiribati
Korea
Kosovo
Kuwait
Kyrgyzstan
Liberia
Libya
Libyan Arab Jamahiriya
Lithuania
Luxembourg
Macau
Madagascar
Malawi
Malaysia
Maldives
Mali
Malta
Marshall Islands
Martinique
Mauritania
Mauritius
Mayotte
Micronesia
Midway Islands
Moldova
Monaco
Mongolia
Montenegro
Montserrat
Morocco
Morocco
Mozambique
Netherlands
New Caledonia
Nicaragua
Niger
Nigeria
Niue
Norfolk Island
North Korea
North Macedonia
Northern Mariana Islands
Palestine
Papua New Guinea
Paraguay
Philippines
Qatar
Reunion
Saint Helena
Saint Kitts and Nevis
Saint Lucia
Saint Pierre and Miquelon
Saint Vincent and The Grenadines
Samoa
Sao Tome and Principe
Saudi Arabia
Senegal
Serbia
Seychelles
Sierra Leone
Singapore
Slovenia
Solomon Islands
Somalia
South Africa
South Korea
South Sudan
Spain
Sri Lanka
Sudan
Suriname
Switzerland
Syria
Taiwan
Tajikistan
Tanzania
Thailand
Timor Leste
Timor-Leste
Togo
Trinidad and Tobago
Tunisia
Turkey
Turkmenistan
Turks and Caicos Islands
Tuvalu
Ukraine
United Arab Emirates
Uruguay
Uzbekistan
Vanuatu
Venezuela
Vietnam
Wake Island
Wallis and Futuna
Western Sahara
Yemen
Zambia
Zimbabwe