Page:CAB Accident Report, Delta Air Lines Flight 8715.pdf/6

- 6 - but the flight engineer had apparently reached it first. It is believed, however, that this valve was in the down position at the time.

It is significant that the crew apparently did not use the hydraulic brakes, the auxiliary hydraulic pump, or the emergency air brake system in attempting to stop the aircraft.

Prior to turning right on the military ramp the pilot would have used the normal hydraulic braking to slow the aircraft. Had the brakes not been working at this time the captain would have, most probably, said that the brakes were not working. At this time either he or the first officer should have turned on the auxiliary hydraulic pump which would have built up pressure for the brakes only and the aircraft could have been stopped. This would have occurred prior to reaching the military ramp and prior to starting the turn to the right on the ramp.

Neither of the surviving crew members could remember if they felt any deceleration which could be associated with brake application; nor could they state that they noticed the captain attempting to use the brakes. The only thing they remembered was that the captain was trying to use the nose steering wheel and their interpretation of his statement was that he couldn't steer the aircraft. Therefore, it must be assumed that the normal hydraulic brakes were never used after turning onto Taxiway "D" and prior to striking the parked aircraft. No explanation can be found as to why the brakes were not used. There is also no valid explanation for the failure of the first officer to use the brakes available to him to aid in stopping the aircraft when he saw the imminent collision. He assumed that since the captain allegedly could not steer the airplane then there was no pressure for using the brakes. While he stated that he reached for the hydraulic bypass handle to check its position he also stated that he did not check the hydraulic pressure gauge to see if he actually had hydraulic system pressure. In addition, he made no attempt to turn on the auxiliary hydraulic pump to get brake pressure. The switch for this pump is located on his side panel adjacent to his right hand.

It is significant that neither of the surviving crew members, by their own admission, monitored the hydraulic system pressure gauge from the time the engines were started until the collision occurred. The Board can only conclude that the flight crew was not paying reasonable attention to the operation of the aircraft during taxi.

The next item to be considered is the captain's failure to utilize the emergency air brakes to make an emergency stop rather than attempting to use propeller reversing. It is a know fact that reversing is relatively ineffective at speeds below 50-60 knots. Use of the air brakes provides immediate braking action and will actually lock the wheels, stopping the aircraft more rapidly than with the use of normal hydraulic brakes.

It is difficult to understand why the crew did not hear and respond to two important radio transmissions by the ground controller. One of these transmission gave additional taxi instructions, the other was a caution message. This would indicate that the crew was not paying attention to the radio and must have been preoccupied in the cockpit.