Narrative:

Large transport was on a VFR approach to runway 26R in denver when a )WX) balloon appeared directly in front of the large transport. The captain was flying and he took evasive action (dove 300 ft) in order to avoid a collision with the balloon. Although the balloon was the cause of the evasive action it was not the event that was of primary concern to the crew at the time. The large transport was turned onto the final approach course 3 1/2 mi behind an heavy transport which was making a visual approach to runway 26L in denver. The 2 runways (26L and 26R) are separated by about 1000 ft. Since the wind at the airport was out of the south (190/11 KTS) the captain felt it best to increase the spacing on the heavy aircraft and the large transport slowed to approach speed. The large transport received a 'traffic, traffic' warning on its TCASII system. The radar screen showed that the warning was triggered by an aircraft 1400 ft above the large transport and directly behind it. The large transport crew asked the denver tower if there was an aircraft behind it and was notified that a commercial medium large transport type aircraft was behind the large transport making a visual approach to runway 26L. The last reading the large transport crew saw of the aircraft following it was 200 ft above and directly behind. As the aircraft following the large transport approached the large transport's position, the captain increased the large transport speed in order to avoid being overrun by the medium large transport. The TCASII gave an oral emergency notification 'climb, climb' and called for a climb of 3500 FPM to avoid a collision with another aircraft. A silver sphere appeared in the windscreen of the flight (it looked like a single engine fighter type aircraft with a single trailing exhaust) and the captain instinctively dove the large transport 300 ft to avoid a collision. In the split second available to the captain to decide what to do in this situation he feels that his visual clues overpwred the TCASII warning. The object turned out to be a large (5 ft in diameter) silver balloon (WX?) with a trailing rope. Subsequent inquiry with denver tower confirmed that WX balloons are released from the denver airport but the large transport crew was unable to find out if a balloon had been released around the time of the incident. Also the crew was unable to find out if WX balloons are equipped with transponders. If they are, perhaps the balloon triggered the TCASII warning. If this crew had not encountered the balloon this report would still be a justifiable NASA report. Allowing simultaneous visual approachs to runways 26 at the denver airport should be reconsidered.

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Original NASA ASRS Text

Title: ACR LGT SPD DEV AND ALT DEV EXCURSION FROM CLRNC ALT ON VISUAL APCH TO DEN.

Narrative: LGT WAS ON A VFR APCH TO RWY 26R IN DENVER WHEN A )WX) BALLOON APPEARED DIRECTLY IN FRONT OF THE LGT. THE CAPT WAS FLYING AND HE TOOK EVASIVE ACTION (DOVE 300 FT) IN ORDER TO AVOID A COLLISION WITH THE BALLOON. ALTHOUGH THE BALLOON WAS THE CAUSE OF THE EVASIVE ACTION IT WAS NOT THE EVENT THAT WAS OF PRIMARY CONCERN TO THE CREW AT THE TIME. THE LGT WAS TURNED ONTO THE FINAL APCH COURSE 3 1/2 MI BEHIND AN HVT WHICH WAS MAKING A VISUAL APCH TO RWY 26L IN DENVER. THE 2 RWYS (26L AND 26R) ARE SEPARATED BY ABOUT 1000 FT. SINCE THE WIND AT THE ARPT WAS OUT OF THE S (190/11 KTS) THE CAPT FELT IT BEST TO INCREASE THE SPACING ON THE HVY ACFT AND THE LGT SLOWED TO APCH SPD. THE LGT RECEIVED A 'TFC, TFC' WARNING ON ITS TCASII SYS. THE RADAR SCREEN SHOWED THAT THE WARNING WAS TRIGGERED BY AN ACFT 1400 FT ABOVE THE LGT AND DIRECTLY BEHIND IT. THE LGT CREW ASKED THE DENVER TWR IF THERE WAS AN ACFT BEHIND IT AND WAS NOTIFIED THAT A COMMERCIAL MLG TYPE ACFT WAS BEHIND THE LGT MAKING A VISUAL APCH TO RWY 26L. THE LAST READING THE LGT CREW SAW OF THE ACFT FOLLOWING IT WAS 200 FT ABOVE AND DIRECTLY BEHIND. AS THE ACFT FOLLOWING THE LGT APCHED THE LGT'S POS, THE CAPT INCREASED THE LGT SPD IN ORDER TO AVOID BEING OVERRUN BY THE MLG. THE TCASII GAVE AN ORAL EMER NOTIFICATION 'CLB, CLB' AND CALLED FOR A CLB OF 3500 FPM TO AVOID A COLLISION WITH ANOTHER ACFT. A SILVER SPHERE APPEARED IN THE WINDSCREEN OF THE FLT (IT LOOKED LIKE A SINGLE ENG FIGHTER TYPE ACFT WITH A SINGLE TRAILING EXHAUST) AND THE CAPT INSTINCTIVELY DOVE THE LGT 300 FT TO AVOID A COLLISION. IN THE SPLIT SECOND AVAILABLE TO THE CAPT TO DECIDE WHAT TO DO IN THIS SITUATION HE FEELS THAT HIS VISUAL CLUES OVERPWRED THE TCASII WARNING. THE OBJECT TURNED OUT TO BE A LARGE (5 FT IN DIAMETER) SILVER BALLOON (WX?) WITH A TRAILING ROPE. SUBSEQUENT INQUIRY WITH DENVER TWR CONFIRMED THAT WX BALLOONS ARE RELEASED FROM THE DENVER ARPT BUT THE LGT CREW WAS UNABLE TO FIND OUT IF A BALLOON HAD BEEN RELEASED AROUND THE TIME OF THE INCIDENT. ALSO THE CREW WAS UNABLE TO FIND OUT IF WX BALLOONS ARE EQUIPPED WITH TRANSPONDERS. IF THEY ARE, PERHAPS THE BALLOON TRIGGERED THE TCASII WARNING. IF THIS CREW HAD NOT ENCOUNTERED THE BALLOON THIS RPT WOULD STILL BE A JUSTIFIABLE NASA RPT. ALLOWING SIMULTANEOUS VISUAL APCHS TO RWYS 26 AT THE DENVER ARPT SHOULD BE RECONSIDERED.

Data retrieved from NASA's ASRS site as of July 2007 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.