Narrative:

A recent procedure change required setting a variable flap 'gate' at 23 degrees (for increase drag in dscnts) instead of stowed. Normal flap setting sequence for landing 15 degree slats, 0 degree flaps, slats, 11 degree flaps, slats, 15 degree flaps, and landing slats, flaps 28 degrees or 40 degrees. I was flying a night visual to runway 05 (ILS was turned on for runway 23). Starting final approach descent gear was up, slats and 15 degree flaps. After gear was lowered I asked for 28 degree flaps and before landing checklist. Captain and I both thought gear was down with 28 degree flaps and land slats. About 200 ft AGL the GPWS came on and I thought it was for the GS as I had the runway 05 ILS in. But it was for flaps. Actually we had 23 degree flaps and takeoff slats as evidenced by a green takeoff light vice a blue land light. The difference between 23 degrees and 28 degrees is very difficult to see on the gage. I immediately began a go around and the captain lowered the flap handle out of the 23 degree (new) detent to 28 degrees. A landing was made to runway 23 without further incident. I sensed something was wrong on final because I couldn't get aircraft to 28 degree final speed. I even rechked the confign and didn't catch it. I am really attuned to the slat takeoff and land lights now. Potential problem. At same time of this procedure change the single engine go around procedure is to use flaps 11 degrees instead of 15 degrees. If flaps greater than 15 degrees are selected and a single engine go around is initiated flaps used to go to 15 degrees where there is a gate so less flaps cannot be inadvertently selected. There is not much difference between the 15 degree gate and 11 degree. Someone on a single engine go will raise the flaps and end up in the dirt. Callback conversation with reporter revealed the following information: this md-88 first officer reports a problem with a recent change of procedure at his air carrier. To answer a need for more drag so that the low-drag md-88 could descend more steeply at the lower pattern airspds this company has decided to use the dial-a-flap system to select flaps 23 degrees instead of the preset gates of 15 or 28 degrees in this same general area. 23 degrees provides more drag than 15 degrees and yet stays above the continuous warning horn that would sound with flaps at 28 degrees with the landing gear up. Until this procedure change the dial-a-flap selector was set at 0 degrees and the factory installed flap detents were used for all flap settings. The reporter said that since the new procedure began, the incidents of flap selection errors have become frequent. This first officer has an extensive backgnd in human factors studies and he has talked to his flight department mgrs, but they do not think that there is a problem. The first officer is now in training on another aircraft and said that the flap procedure is, in part, his reason for leaving the md-88. The other change of procedure for use of the flaps is to select flaps 11 degrees instead of flaps 15 degrees. The 11 degree setting will provide a bit less drag, but an error in placing the selector in the 11 degree detent could allow the flaps to retract during the go around if the flap handle was placed above the 11 degree detent. The flaps would be driven up by air pressure as the aircraft accelerated. This is a single engine go around procedure only, but single engine acceleration is slow enough that the flap retraction force may have a much greater effect than if both engines were available. The acceleration curve in a both engine operating go around may be fast enough to stay ahead of stall speeds even at heavy gross weights.

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Original NASA ASRS Text

Title: AIRLINE MGMNT POLICY -- AIRLINE OPERATIONAL PROC -- THIS FO BELIEVES THAT A PROC CHANGE BY HIS ACR IS LESS SAFE THAN THE OLD PROC.

Narrative: A RECENT PROC CHANGE REQUIRED SETTING A VARIABLE FLAP 'GATE' AT 23 DEGS (FOR INCREASE DRAG IN DSCNTS) INSTEAD OF STOWED. NORMAL FLAP SETTING SEQUENCE FOR LNDG 15 DEG SLATS, 0 DEG FLAPS, SLATS, 11 DEG FLAPS, SLATS, 15 DEG FLAPS, AND LNDG SLATS, FLAPS 28 DEGS OR 40 DEGS. I WAS FLYING A NIGHT VISUAL TO RWY 05 (ILS WAS TURNED ON FOR RWY 23). STARTING FINAL APCH DSCNT GEAR WAS UP, SLATS AND 15 DEG FLAPS. AFTER GEAR WAS LOWERED I ASKED FOR 28 DEG FLAPS AND BEFORE LNDG CHKLIST. CAPT AND I BOTH THOUGHT GEAR WAS DOWN WITH 28 DEG FLAPS AND LAND SLATS. ABOUT 200 FT AGL THE GPWS CAME ON AND I THOUGHT IT WAS FOR THE GS AS I HAD THE RWY 05 ILS IN. BUT IT WAS FOR FLAPS. ACTUALLY WE HAD 23 DEG FLAPS AND TKOF SLATS AS EVIDENCED BY A GREEN TKOF LIGHT VICE A BLUE LAND LIGHT. THE DIFFERENCE BTWN 23 DEGS AND 28 DEGS IS VERY DIFFICULT TO SEE ON THE GAGE. I IMMEDIATELY BEGAN A GAR AND THE CAPT LOWERED THE FLAP HANDLE OUT OF THE 23 DEG (NEW) DETENT TO 28 DEGS. A LNDG WAS MADE TO RWY 23 WITHOUT FURTHER INCIDENT. I SENSED SOMETHING WAS WRONG ON FINAL BECAUSE I COULDN'T GET ACFT TO 28 DEG FINAL SPD. I EVEN RECHKED THE CONFIGN AND DIDN'T CATCH IT. I AM REALLY ATTUNED TO THE SLAT TKOF AND LAND LIGHTS NOW. POTENTIAL PROB. AT SAME TIME OF THIS PROC CHANGE THE SINGLE ENG GAR PROC IS TO USE FLAPS 11 DEGS INSTEAD OF 15 DEGS. IF FLAPS GREATER THAN 15 DEGS ARE SELECTED AND A SINGLE ENG GAR IS INITIATED FLAPS USED TO GO TO 15 DEGS WHERE THERE IS A GATE SO LESS FLAPS CANNOT BE INADVERTENTLY SELECTED. THERE IS NOT MUCH DIFFERENCE BTWN THE 15 DEG GATE AND 11 DEG. SOMEONE ON A SINGLE ENG GO WILL RAISE THE FLAPS AND END UP IN THE DIRT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS MD-88 FO RPTS A PROB WITH A RECENT CHANGE OF PROC AT HIS ACR. TO ANSWER A NEED FOR MORE DRAG SO THAT THE LOW-DRAG MD-88 COULD DSND MORE STEEPLY AT THE LOWER PATTERN AIRSPDS THIS COMPANY HAS DECIDED TO USE THE DIAL-A-FLAP SYS TO SELECT FLAPS 23 DEGS INSTEAD OF THE PRESET GATES OF 15 OR 28 DEGS IN THIS SAME GENERAL AREA. 23 DEGS PROVIDES MORE DRAG THAN 15 DEGS AND YET STAYS ABOVE THE CONTINUOUS WARNING HORN THAT WOULD SOUND WITH FLAPS AT 28 DEGS WITH THE LNDG GEAR UP. UNTIL THIS PROC CHANGE THE DIAL-A-FLAP SELECTOR WAS SET AT 0 DEGS AND THE FACTORY INSTALLED FLAP DETENTS WERE USED FOR ALL FLAP SETTINGS. THE RPTR SAID THAT SINCE THE NEW PROC BEGAN, THE INCIDENTS OF FLAP SELECTION ERRORS HAVE BECOME FREQUENT. THIS FO HAS AN EXTENSIVE BACKGND IN HUMAN FACTORS STUDIES AND HE HAS TALKED TO HIS FLT DEPT MGRS, BUT THEY DO NOT THINK THAT THERE IS A PROB. THE FO IS NOW IN TRAINING ON ANOTHER ACFT AND SAID THAT THE FLAP PROC IS, IN PART, HIS REASON FOR LEAVING THE MD-88. THE OTHER CHANGE OF PROC FOR USE OF THE FLAPS IS TO SELECT FLAPS 11 DEGS INSTEAD OF FLAPS 15 DEGS. THE 11 DEG SETTING WILL PROVIDE A BIT LESS DRAG, BUT AN ERROR IN PLACING THE SELECTOR IN THE 11 DEG DETENT COULD ALLOW THE FLAPS TO RETRACT DURING THE GAR IF THE FLAP HANDLE WAS PLACED ABOVE THE 11 DEG DETENT. THE FLAPS WOULD BE DRIVEN UP BY AIR PRESSURE AS THE ACFT ACCELERATED. THIS IS A SINGLE ENG GAR PROC ONLY, BUT SINGLE ENG ACCELERATION IS SLOW ENOUGH THAT THE FLAP RETRACTION FORCE MAY HAVE A MUCH GREATER EFFECT THAN IF BOTH ENGS WERE AVAILABLE. THE ACCELERATION CURVE IN A BOTH ENG OPERATING GAR MAY BE FAST ENOUGH TO STAY AHEAD OF STALL SPDS EVEN AT HVY GROSS WTS.

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.