B757-200
Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Took Evasive Action
Human Factors
I was near the APU exhaust during my walkaround and my ears perked up when I heard the APU change pitch (obviously unloading). Wondering if someone had turned off the aircraft packs I continued forward to the left main gear for my preflight. Somewhat alerted by this abnormality; I then noticed the left engine spooling up just before I would have walked behind it. I saw that the aircraft beacon wasn't on and; having no indication maintenance was around; I ran up to the cockpit.When I got there; I saw maintenance in the process of shutting the engine down; and I confronted them about the unannounced engine start with myself and other ground crew beneath the plane. They acknowledged they had made a mistake and apologized for not letting us know about the engine motoring that needed to be done. They then turned on the beacon and continued their procedure. I went back outside and informed the crew chief; who had been standing behind the right engine the whole time; to let his people know about more possible maintenance actions. He was surprised to hear what had happened. In addition to ground crew and equipment behind the right engine; the fuel truck had also been hooked up to the plane during this event.Obviously; this was an error in maintenance procedures and not an intentional action by maintenance. The Captain also spoke with the two mechanics after they were done and said they were very contrite and apologetic. While it is easy to get desensitized to many things happening on & around an aircraft simultaneously; prudently adhering to normal procedures and common-sense communication would have prevented this extremely unsafe event.
B757-200 First Officer (FO) reported he noticed during walkaround in LAX that maintenance started an engine without clearing the area.