Ramp - Ground Handling -- Common Mode Failure
In messages #2 & #8 above, the writer outlined the safety advantages of VOICE communication during PUSHBACK.
Then comes this odd case (maybe not so odd), where the initiating-failure [separation of the TowBar], also disabled the safety-feature [voice communication], P.C. "final" recently released by the NTSB:
Untitled Page "... February 20, 2011, at 1924 central ... Boeing 737-823, N945AN, that was being pushed back from its gate at the Dallas [DFW] ... struck a parked ... MD-82 ... N70504.... DC-9-82 was substantially damaged....
"... the 737 was being pushed straight back from gate A26 when the tow bar separated from the nose gear. The airplane rolled backwards, severing the communications cord to the flight deck. The captain and first officer, who were in the process of starting the engines, were unaware that the airplane was rolling freely. The 737's right wing tip struck the nose of the DC-9 that was parked at pad N. ..."
[And you thought that this scenario (GCOL-Grnd Collision while rolling backwards) at DFW was most likely because of the Power-back operations conducted by operators' unlicensed ground employees at DFW. During pushback, after the TowBar separated, the Interphone cord fractured, so Voice communication to the pilots was not possible. This resulted in an airliner moving backwards, toward another airliner, with pilots unaware of either failure.]
Edited -- to show images from NTSB's "docket"
In the past few years, the NTSB's website offers readers a web-link to their "docket". For minor mishaps, the "docket" sometimes provides the reader with a better mishap-review (better than the NTSB's P.C. "final" & "narrative"). This web access is new, and there are good reason that a company and a pilots' association should object (since in the past "docket" information was not so easily available for public view). For this mishap, the "docket" includes a better review of this Pushback GCOL, with photos, graphics, and analysis of the towbar failure-interactions that initiated the release of the aircraft from the towbar; download the 18-pg pdf:
"... When separation occurred approximately 139’ after the pushback began, communication with the cockpit was lost as the
communication cord was stretched and snapped from the interphone connection. During this approximately 38 seconds, the cockpit crew was engaged in starting the engines for taxi. Per interviews with the Captain and First Officer of the flight, both had their attention on starting the engines and
did not realize the aircraft was rolling unattached to the pushout tractor until just before impact with N504. Having both crew members engaged in starting the engines on the 737 aircraft is the standard procedure....
From "docket", NTSB mishap-rpt-form, pg 10,
"... aircraft continued to roll and struck ... MD80 parked ... RH wingtip of N3BY (737) went over ckpt window of N504 and rested on crown skin...."
Excerpt from pg 4 of the company-review, in the NTSB "docket":
"Recommendations:
1. Explore the feasibility of a procedural change in engine start up on the 737 aircraft to allow one cockpit crewmember to engage in engine start while the other crewmember maintains heads up situation awareness of the aircraft during pushback/ towing operations.
2. Study if wireless ground to cockpit communication could be implemented to ensure constant communication with the cockpit."