Date: 201402
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: Mixed
Weather elements / visibility: 2.5
Light: Daylight
Aircraft: B737-300
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Aircraft component: Cargo Door
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Human factors: Situational Awareness; Communication Breakdown
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Gate; Flight Crew Rejected Takeoff; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Human Factors; Aircraft
Primary problem: Human Factors

Narrative: I was PF on takeoff after deicing. Weather at the time was reporting visibility of 2NM -SN; winds 020/12. My attention was outside when the 80 knot callout was made. It was about this time that I also saw a Master Caution light. I do not remember the Captain stating intention to 'continue' or 'reject; I have the aircraft.' I glanced up briefly and stated 'aft cargo door.' I believe it was at this point I might have led the Captain down the path of rejecting the takeoff. The reject was uneventful and I noted a speed of 100 knots on the airspeed indicator. After notifying ATC; we taxied off the active runway on the reverse high speed Taxiway. After calculating the RTO [energy]; we used a conservative number of a three-mile taxi which gave us a 30-minute cooling period before entering the gate area.  Neither the flight attendants nor the passengers seemed alarmed by the rejection. Verbalization of intention to 'continue' or 'reject' needs to be stated clearly and immediately. Looking back now; knowing it was only a Master Caution and around 80 knots; I would have been better off noting the indication to myself and addressing it once airborne to prevent any confusion in the future.


Second narrative: Close to 80 KIAS; Master Caution illuminated. The F/O called out 'aft cargo door open.' Since 80 KIAS call had not been made; the Captain assumed control and rejected the takeoff. During the reject; 100 KIAS was noted. Originally; the Captain was thinking continue but the unique timing and further input from the F/O added information which ended in a reject decision instead. Upon returning to the gate; Ground Ops discovered they had left a strap for closing the door hanging out of the aft cargo door. The reject and follow on procedures were fine and the flight departed normally later after procedures; maintenance; and dispatching. While the aircraft was not damaged; in hindsight; it would seem continuing would have been the right decision. Also; making the 80 KIAS call even if incident occurs simultaneously is important. The intent was this was a prior to 80 KIAS abort in reality 100 KIAS was noted.Train Captains to clearly verbalize intentions immediately with inputs and that they may need to stay with the decision even with other crew inputs. Practice the PNF reject duties as Captain in training. Standardize verbiage for malfunctions on takeoff possibly similar to callouts.


Synopsis: B737-300 flight crew experiences an aft cargo door warning at 80 KTS during takeoff with the First Officer flying. When the Captain says nothing; the First Officer announces the warning and the Captain rejects. Maintenance found a strap hanging out of the door.