I don't know how to thank you all enough. After the clue regarding vam_live_acars and vam_live_flights tables, I checked each and every line of the .phps and found that strangely my Live Flights were not updating because the table 'vam_live_flights' id field was not defined to have AUTO_INCREMENT !!!
That's why the query to insert into this table was failing. I added the AUTO_INCREMENT and voila it worked lovely. Thanks so much.
Just for reference I'm giving the right sql to create the 'vam_live_flights' table, just in case someone gets stuck with similar issue.
Correct table vam_live_flights
-----------------------------------
CREATE TABLE IF NOT EXISTS `vam_live_flights` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`gvauser_id` int(11) NOT NULL,
`flight_id` varchar(200) NOT NULL,
`departure` varchar(4) NOT NULL,
`arrival` varchar(4) NOT NULL,
`ias` int(11) NOT NULL,
`heading` int(11) NOT NULL,
`gs` int(11) NOT NULL,
`altitude` int(11) NOT NULL,
`fuel` int(11) NOT NULL,
`fuel_used` int(11) NOT NULL,
`latitude` double NOT NULL,
`longitude` double NOT NULL,
`time_passed` int(11) NOT NULL,
`perc_completed` int(11) NOT NULL,
`time_flag` timestamp NULL DEFAULT NULL,
`oat` int(11) NOT NULL,
`wind_deg` int(11) NOT NULL,
`wind_knots` int(11) NOT NULL,
`flight_status` varchar(50) NOT NULL,
`last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;
ALTER TABLE
`vam_live_flights`
ADD
`plane_type` VARCHAR(4) NULL;
ALTER TABLE
`vam_live_flights`
ADD
`pending_nm` INT NULL;
ALTER TABLE `vam_live_flights` ADD `network` VARCHAR(50) NULL DEFAULT NULL;
Thanks a lot everyone for providing correct clue.

Warm Regards
Amit Pandit