Air India Flight 829 was scheduled to operate flight from Mumbai to Riyadh. Prior to the flight from Mumbai both the commander and the First officer obtained a briefing and proceeded for the flight. There were 213 passengers and 16 cabin crew members onboard. The APU was under MEL and therefore engine #4 was started at bay #63 prior to pushback. After some ATC delay the push back commenced at around 05:19 UTC. The tow bar failed after the aircraft had moved just 8-10 feet. After arranging a new tow bar the push back was completed facing east and rest of the 3 engines were started in the sequence of 3, 2, 1. The aircraft started taxing at around 05:24 UTC and turned to taxiway G. While taxing on G, a company aircraft operated was docked on Bay 95, saw the gushing of fuel around left hand side engine of VT-ESM and immediately informed to dispatch on the company channel about the fuel leak. The captain of this aircraft could not contact VT-ESM since he was on the ground frequency and VT-ESM had already changed over to tower frequency. The dispatcher called AI-829 on company channel to inform about the fuel leak; however the VHF 3 (company channel) was kept in the off position by the operating crew since it creates a lot of disturbance during briefing and taxi/takeoff clearances. This was in non-conformance with the company operating procedures. While the aircraft was taxing on G, the engineer who was allocated on the other company aircraft also saw the fuel leak from No 1 engine of the aircraft and took off his ramp jacket and started signaling to the aircraft. The Cabin crew in-charge (CCIC) did see the person signaling but could not figure out the reason and hence ignored the same. The “follow me” jeep in the vicinity noticed the fuel leak and informed ATC immediately to switch off the engine. The jeep driver could only tell the registration to ATC. As the aircraft turned on to taxiway A3, ATC gave a call for VT-ESM twice. However there was no reply from the aircraft. Then the ATC called IC-629 confirming their registration as ESM which they said negative. Finally ATC (SMC controller) called out AI-829 to verify its registration being ESM, which was confirmed by the crew. Then ATC informed that as per the “follow me” jeep there was a heavy fuel leak from the left engine of the aircraft and gave instructions to switch off the engines immediately. The commander started the emergency checklist. By the time, the engine no.1 already caught fire and started progressing towards engine no. 2. The CCIC saw the fire while getting up from her located position and immediately gave evacuation commands on the PA (evacuation from the right). The passengers by now had also noticed fire from the cabin windows and rushed towards the door. The crew managed the passengers and deployed the right hand side escape slides. All the passengers and the crew evacuated the aircraft safely. After ensuring nobody was left behind inside the aircraft CCIC evacuated the aircraft. Since the cockpit is on the upper deck, both the pilots evacuated from the upper deck and did not come down to the lower deck during evacuation. They also came out before evacuation was completed. In the process of emergency evacuation there was minor injury to 21 passengers of the aircraft and were given first aid and then shifted to AI hospital. By the time the fire vehicles had reached the aircraft and sprayed foam to put off the fire. Two of the fire men climbed the escape slide from the right hand side and went onboard the aircraft to check for any passengers left behind during the evacuation. They in fact opened the left hand side doors as there was fume and smell inside and hence the left hand side slides were deployed by the firemen after the evacuation was carried out by the cabin crew. The incident took place at about 0530 UTC under day light condition and there was drizzling. Aircraft was damaged on the left hand side due to fire. CAUSE: Complete dislodging of No. 1 strut fuel feed line coupling due to dislodging of tie wire from the failed tie wire hole is the cause for heavy fuel leak and leaked fuel falling on hot #1 engine resulted into fire. Contributory factors: 1. Not tightening the coupling to the proper specification and procedure during maintenance resulting into ductile failure of coupling material is the main contributory causative factor. 2. Installation , maintenance or environmental variables. 3. Failure of departure AME in adhering to the standard procedures and his perfunctory function. 4. Lapses/failure of the pilots during walk around inspection 5. Non-conformance by the pilots- company operating procedures 6. Failure of ATC-SMC personnel for prompt and effective handling emergency situation. 7. Lack of situational awareness and crew coordination.