I know, the flaps shouldn’t go asymetric, but sometimes they just do. http://avherald.com/h?article=45a126c3
But landing with the flaps retracted or near-retracted is a trickier deal, since now they have to land at a much higher deck angle at much higher speeds, even after lowering their landing weight.
So the "flight control problem" they declared an emergency for was not so much because of asymmetrical flaps as it was for the lack of the ability to lower their flaps for landing.
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When I think of a serious "asymmetric flap" problem, this scenario is what comes to mind -- classic worst case, required some extraordinary airmanship to survive:
On the night of June 16, 2002, Capt. James Almlie and First Officer Mark Abbott were the pilots of a FedEx MD-11 flight from Bangkok, Thailand, to Subic Bay International Airport in the Philippines. Nearing the turn onto final approach at approximately 1,500 feet, Capt. Almlie, the pilot flying, called for flaps 50 for landing.
As F/O Abbott moved the flap handle to that position, the pilots heard a loud BANG! and felt the airplane immediately and rapidly roll to the left. Capt. Almlie immediately countered the uncommanded roll and leveled the wings, which required nearly full right aileron.
F/O Abbott immediately called for a go-around, while Capt. Almlie fought to maintain control of the airplane. The pilots complied with the go-around procedures as best they could, but found that the outboard flaps retracted to 28 degrees while the inboard flaps were stuck in an asymmetric position, somewhere between 41 and 50 degrees.
The pilots diverted to Manila’s Nino Aquino International Airport. They completed emergency procedures for the failures for which they were receiving alerts and other indications from the cockpit instruments and warning systems—namely, asymmetric flaps/slats, and failure of hydraulic system No. 3.
Having become unwilling test pilots flying an airplane well outside its certification parameters, Capt. Almlie and F/O Abbott continued to work as a team and safely navigated the barely controllable airplane around the mountainous terrain of the Philippine archipelago in the darkness. At one point, the control forces required to keep the wings level (estimated by the pilots to be 40-50 pounds of force) became so great that Capt. Almlie had to hand over the controls to F/O Abbott and allow himself a break before beginning the approach to Manila. The pilots flew an ILS approach to Runway 6 with Capt. Almlie on the flight controls and F/O Abbott handling the throttles. (Because of the abnormally high amount of drag on the airplane, the autothrottles did not react quickly enough.) Working together in this unusual but effective way, they brought the crippled airplane to a safe but hardly uneventful landing.
The pilots’ subsequent walk-around revealed that the left inboard flap had become detached from the wing because of structural failure of bolts in the attachment assembly. The violent failure severed hydraulic lines in the left wing, which led to the failure of one hydraulic system.
Debris from the damaged components had caused the ground spoiler system to deploy and jam in the "up" position, destroying much of the lift on the left wing. Because of the amount of control deflection required to counter the loss of lift on the left wing, spoilers also deployed on the right wing, robbing that wing of lift as well........ F/O Abbott said he was alive "by the grace of God. We were so much on the edge, every time we went through clouds or hit turbulence, with full right yoke, the airplane would go to the left," with mountains only a mile and a half away in that direction.
"I felt like angels were holding us up," he declared. "I feel very fortunate to be alive."
http://www.alpa.org/portals/alpa/magazine/2004/Jan2004_AirSafetyAwards.htm