Date: 201603
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate
Result: Flight Crew Took Evasive Action
Contributing factors: Company Policy; Procedure; Equipment / Tooling
Primary problem: Ambiguous

Narrative: After we were marshaled into the gate we shutdown normally. The Agent made several attempts to position the jetway up to the aircraft for passenger deplaning. While all of this was ongoing; the provisioning trucks approached the aircraft front and rear. The FAs disarmed the doors; and then opened the doors for Provisioning to enter the aircraft and begin their duties.The aircraft has been sitting at the gate for approximately ten plus minutes and the jetway had still not been positioned up to the aircraft for passenger deplaning. I was advised by the ground crew that the jetway had malfunctioned and we would have to be towed to another gate. The jetway was stuck approximately ten feet from the aircraft.My concerns are the fact that we now have to tow my aircraft to another gate; we have to get all passengers reseated; luggage stowed; doors rearmed; not to mention the jetway is now positioned in the safety zone. The other area of concern is; during our time at the gate; which was approximately 20 minutes; we had no way to evacuate my passengers and crew due to the fact that the L-1 door is not available due to the malfunction of the jetway; the L-2 and rear door were unavailable due to the fact the provisioning trucks were against the aircraft and the doors were open.My FAs were very concerned about the safety aspects; due to the fact all of our doors were unarmed and the only possible way was to evacuate our passengers; if there was an emergency; would be the 'over-wing exits' where it would have been impossible to reposition the flaps; thus causing an unsafe condition for the passengers and crew to slide down the wing of the aircraft.In my career; I unfortunately had an evacuation with several injuries due to the fact that several passengers attempted to slide off of the front of the wing instead of the rear of the wing as briefed by the FAs. So; I have some experience regarding what can happen in an evacuation.In short; the provisioning trucks should never approach the aircraft until the jetway is attached to the aircraft with the L-1 door open so as to provide a safe egress point for passengers and crew to exit. Once the provisioning truck enters the safety zone and moves towards the aircraft it renders the emergency evacuation slides inoperative for that door.When you park at a gate after landing; and all of your exits are blocked; leaving just the over-wing exits; you have greatly diminished; if not eliminated; the margin of safety for your passengers and crew; should the need arise to have an emergency evacuation.The two scenarios that could possibly warrant an emergency evacuation could be an overheated brake; causing a fire; or a possible APU fire. The over wing exits would be the only egress point due to the provisioning trucks in the front and rear of the aircraft; which would be the last resort to use due to the location of the APU and brakes. I spent almost 20 minutes where I had almost no way to evacuate this aircraft; due to the fact my exits were either blocked or not available.Maybe we should reconsider our provisioning procedures for arriving aircraft. After speaking with the agent and the provisioning crews; their only concern was to get to the aircraft ASAP as their time was limited to get the aircraft serviced; there seemed to be little concern; whatsoever; as to my safety concerns that my doors and our evacuation slides were rendered inoperative due to the provisioning trucks. The explanation I received was 'this is the way we have always done it'. I understand that everyone has a job to do in a timely manner; but this normal operation turned abnormal due to a jetway malfunction. I; as Captain of this flight; am responsible for the safety of my passengers and crew; until everyone is safely off of the aircraft; and my decision to have the provisioning trucks immediately removed when I felt we were in an unsafe condition should have been obeyed; it's simple as that.I see this similar situation at almost every provisioning station where the truck pulls up to the front and sometimes the rear of the aircraft the moment the brake is set with engine shutdown; thus eliminating any type of emergency evacuation from the front and possibly the rear of the aircraft until the jetway is attached. I have mentioned this at several stations and the agents look like they do not understand why there could be a problem.Review our arrival procedures pertaining to our provisioning operations so as to provide a safe environment for everyone including the provisioning staff as well as my passengers and crew all options to ensure we have every opportunity available to evacuate this aircraft due to any unforeseen emergency.




Synopsis: B737 Captain described a situation where his aircraft could not be evacuated at the gate if the jet bridge malfunctions prior to connecting with the aircraft upon arrival. In this situation; with the flaps retracted and catering trucks at two doors; only one door may be available for evacuation and it would have to be armed.