Narrative:

After an unscheduled aircraft swap; ground operations was rushed due to moving baggage for passengers to the unscheduled aircraft. Additionally; due to the lack of cabin bag storage; ground personnel were rushed to load 11 gate-checked bags at push; about 30 minutes late.the push started uneventfully; but as we were clearing the safety zone; the tug driver yelled 'set the brake! Set the brake! Set the brake!' as there was no preface to the call; and ground was talking constantly; I initially didn't know he was talking to me. Of note; we were using the wireless communication set. If you fly at all; you know that the volume output by these units to the cockpit is totally insufficient. I usually have to position the volume knob to three o'clock or higher just to hear the tug driver; and if the first officer speaks on the intercom; or ground is speaking; the tug is nearly impossible to hear. I announced I was setting the brakes in case the call wasn't from my guy; and despite trying to be gentle on the brakes; the aircraft still reared nose up and shuttered to a stop. I guess braking an aircraft while backing up requires an entirely different technique than one moving forward. The tow bar had released from the nose gear connection point and the aircraft was moving all on its own. Thank goodness we weren't in a [longer aircraft]. It could have stood it on its tail.points of note:- [airport] was doing cascading aircraft swaps due to a dent written up on one aircraft. I thought that our policy was to keep the crew with the aircraft they broke in order to only inconvenience the passengers on that aircraft rather than every passenger flying through [this airport]. Unscheduled swaps kill the ramp agents.- the wireless communication sets are impossible to hear without nearly maxing the acp volume. Still normal volume on other channels is louder than wireless. Secondly; and anecdotally at least twice on each four day; some ramp agent has to run and find another set as the wireless is unreliable.- ('set the brakes') three times with no preface on the lowest volume channel causes confusion. We weren't sure we were being called; but felt we needed to stop in case we were about to hit something or someone. The urgency and tenor of the voice demanded immediate action.- flight attendants were up briefing for departure. Once the brakes were set; I interrupted them to inquire about their condition. The a thought the B may have hurt herself. I asked her to find out for sure. No injuries; thankfully.- if ramp agents are trained for a loose aircraft scenario; calm communication such as 'captain; the tow bar has come loose. Please set the brakes' or 'captain; stop for a truck' would create a shared mental model. Not knowing if someone has walked behind the aircraft; or even that the tug is no longer hooked up can lead to injuries or damage to the aircraft.

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Original NASA ASRS Text

Title: B737 Captain reported tow bar had released from the nose gear connection point during pushback; necessitating the gradual use of brakes to bring the aircraft to a stop.

Narrative: After an unscheduled aircraft swap; ground operations was rushed due to moving baggage for passengers to the unscheduled aircraft. Additionally; due to the lack of cabin bag storage; ground personnel were rushed to load 11 gate-checked bags at push; about 30 minutes late.The push started uneventfully; but as we were clearing the safety zone; the tug driver yelled 'Set the brake! Set the brake! Set the brake!' As there was no preface to the call; and Ground was talking constantly; I initially didn't know he was talking to me. Of note; we were using the wireless communication set. If you fly at all; you know that the volume output by these units to the cockpit is totally insufficient. I usually have to position the volume knob to three o'clock or higher just to hear the tug driver; and if the First Officer speaks on the intercom; or ground is speaking; the tug is nearly impossible to hear. I announced I was setting the brakes in case the call wasn't from my guy; and despite trying to be gentle on the brakes; the aircraft still reared nose up and shuttered to a stop. I guess braking an aircraft while backing up requires an entirely different technique than one moving forward. The tow bar had released from the nose gear connection point and the aircraft was moving all on its own. Thank goodness we weren't in a [longer aircraft]. It could have stood it on its tail.Points of note:- [Airport] was doing cascading aircraft swaps due to a dent written up on one aircraft. I thought that our policy was to keep the crew with the aircraft they broke in order to only inconvenience the passengers on that aircraft rather than every passenger flying through [this airport]. Unscheduled swaps kill the ramp agents.- The wireless communication sets are impossible to hear without nearly maxing the ACP volume. Still normal volume on other channels is louder than wireless. Secondly; and anecdotally at least twice on each four day; some ramp agent has to run and find another set as the wireless is unreliable.- ('Set the brakes') three times with no preface on the lowest volume channel causes confusion. We weren't sure we were being called; but felt we needed to stop in case we were about to hit something or someone. The urgency and tenor of the voice demanded immediate action.- Flight attendants were up briefing for departure. Once the brakes were set; I interrupted them to inquire about their condition. The A thought the B may have hurt herself. I asked her to find out for sure. No injuries; thankfully.- If ramp agents are trained for a loose aircraft scenario; calm communication such as 'Captain; the tow bar has come loose. Please set the brakes' or 'Captain; stop for a truck' would create a shared mental model. Not knowing if someone has walked behind the aircraft; or even that the tug is no longer hooked up can lead to injuries or damage to the aircraft.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.