Date: 201501
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: B757-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
ATC / advisory: Ramp ZZZ
Aircraft component: ACARS
Component problem: Design
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Troubleshooting; Human-Machine Interface; Confusion; Distraction
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Dispatch
When detected: Pre-flight
Result: Flight Crew Took Evasive Action; Flight Crew Became Reoriented; Flight Crew FLC Overrode Automation
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: This is more of an FYI regarding the new software being uploaded into the ACARS. During our preflight we got to experience the new software. It took us a few minutes to get familiar with it. Before the flight started; we scrolled through all the screens. One screen in particular caused an issue; it was the screen marked >7500. I don't recall selecting anything; but somehow Dispatch immediately send an ACARS message asking to call him. So I immediately picked up my cell phone and called. He said he received a hijack message absent any info but the flight number and thought it odd since we're at the gate and had barely started boarding. I assured him all was fine and that we were just scrolling through the new ACARS screens. While on the phone with the dispatcher; I tested the DNES button by pushing it; oddly enough; he got no message; so I'm not even sure if that function is active yet.I reviewed the ACARS bulletin associated with this update. It states that a 7500 message is auto sent if you leave the page up for 2 minutes. The only other possibility is the send button marked DNES was pushed which happens to be next to the RETURN to menu button. It's hard to figure because it seemed as if I went through those pages fairly quickly. My best guess that I got interrupted just long enough by the boarding agent; maintenance or the flight attendant. I'm sure this will happen more often as pilots begin to encounter the new software. Personally; I think there should be a requirement to manually SEND such a message and/or the SENT (DNES) button (key 5L) is moved away from the RETURN button (key 6L). I can't imagine a situation wherein you can get to this page; yet not have the extra micro second to hit the SEND button. If the threat was that great; I can assure you that you'd never get to that page to start with. It is also confusing as to what 'DNES' stands for. Why not just label it 'SEND' because such a message should be an assurance of intent.This is a good FYI; because the last thing we need to happen is for someone to be scrolling through the screens enroute and unintentionally leave the >7500 page up while attending to other duties.




Synopsis: A B757 Captain discovered after a new ACARS software installation that when an ACARS screen marked '>7500' is left up for more than two minutes; 7500 code is automatically sent to alert Dispatch of an unwanted situation.