Jan 22 (Reuters) - The U.S. Federal Aviation
Administration has recommended airlines operating Boeing
737-900ER jets inspect door plugs to ensure they are properly
secured after some operators reported unspecified issues with
bolts upon inspections.
    This is an older Boeing model that used a system of
plugs similar to those on the Boeing 737 MAX 9, most of which
have been grounded following the Jan. 5 blowout of a door plug
on an Alaska Airlines MAX 9. 
    Not all the Boeing 737-900ER have the door plugs and all
737-900ERs have had maintenance checks at least once since they
were delivered, so checking them has not had the same urgency. 
    The door plugs - which replace an unused emergency exit -
are most likely to exist on planes with fewer than 189 seats,
above which airlines must use the same space for an active door
in order to provide the right number of evacuation paths.
    Here is a breakdown of Boeing 737-900ER jets currently in
service, with the average number of seats per plane, extracted
from data provided by aviation analytics firm Cirium.
    There are 490 of the planes in service, of which 79 have the
higher-density configuration with 189 or more seats, requiring a
door rather than a plug. Some of the jets have been traded since
they were delivered, meaning they originally had more seats.    
    
 Operator                   Units     Seats        Country
 Alaska Airlines               79          178     US
 Delta Air Lines              160      173-180     US
 El Al                          8          175     Israel
 Fly Baghdad                    3          215     Iraq
 FlyOne                         1          189     Moldova
 Korean Air                     6          173     S Korea
 Lion Air                      58          215     Indonesia
 Mavi Gok                       2          215     Turkey
 Okay Airways                   5          200     China
 Oman Air                       5          183     Oman
 Pegas Fly                      2          215     Russia
 Rossiya Airlines               2          215     Russia
 Smartwings                     2          212     Czech Republic
 Somon Air                      2          184     Tajikistan
 SpiceJet                       1          212     India
 Thai Lion Air                  3          215     Thailand
 Turkish Airlines              15      151-169     Turkey
 United Airlines              136          179     US
                                                   
                                                   
 
 (Reporting by Tim Hepher; Editing by Susan Fenton)