Formula 1 bosses are to ban the use of the DRS overtaking device at the famous Eau Rouge corner at this weekend's Belgian Grand Prix.
Governing body the FIA is concerned that using the device in the flat-out 180mph section could be a safety risk.
The DRS device, which increases top speed by reducing cars' downforce by about 10%, is mainly used on straights.
Race director Charlie Whiting is worried its use on bends could increase the chances of a major crash.
DRS use is limited in races, when drivers can only deploy it on a designated straight if they are less than one second behind the car in front.
The Spa facts
- Spa is considered one of the classic circuits, and, along with Suzuka in Japan and Monaco, the biggest driving challenge still in F1
- The original track was taken off the calendar on safety grounds after 1970
- A shortened version returned in 1983 and has held the Belgian GP ever since, apart from 1984, when it returned to Zolder
- Eau Rouge has been a feature of the Spa track since 1939
But its use is free in practice and qualifying, when drivers are experimenting with car set-ups in pursuit of the best performance.
The FIA is concerned that in pushing the limits, some teams and drivers may take too big a risk. And although safety has improved at Eau Rouge in recent years, the high-speed nature of the track there means any loss of control risks a major accident.
It has emerged that some drivers have been finding DRS complicated to use, and have occasionally become confused as to whether it is being deployed on their car.
The FIA has learned of times when drivers have headed into corners thinking the DRS was not deployed when it fact it was, causing them to battle to keep the car on the track.
The consequences of this happening at Eau Rouge are of significant concern, and are the main reason why the ban has been imposed.
It has only been the last few years when drivers have been able to take Eau Rouge without lifting off the throttle in most circumstances - although it is still not possible to do so at the start of the race on a full tank of fuel.
Before that, they had to judge at what speed the car was capable of taking the corner.
Alonso uses DRS to split the rear wing on his Ferrari
The reason the FIA is reluctant to allow them to go back to this situation, but with the DRS deployed, is the unpredictability and driver uncertainty that has become apparent in its operation.
A technicality has also informed the ban.
As a fail-safe, the DRS is programmed to slot back into high-downforce specification as soon as the driver hits the brakes. But there is no braking into Eau Rouge, so this would not happen.
For these reasons, the FIA has decided to disable DRS throughout the Belgian Grand Prix weekend from the entry to the La Source hairpin, the corner before Eau Rouge, to the top of the hill at the exit of the sequence of corners.
Red Bull driver Mark Webber on the demands of Eau Rouge
“You really don't want to be going off there, even with the increased safety we have these days”
The DRS overtaking zone in the race will start at the exit of Eau Rouge, known as Raidillon, and continue until the braking zone for the Les Combes hairpin at the end of the following straight.
Likened to a roller-coaster ride, Eau Rouge is perhaps the most famous corner in F1 because of its extreme challenge.
Drivers head downhill into it flat-out in top gear. It is a left-right-left sequence of bends that crosses the bottom of a steep valley.
They turn left, then experience huge compression as they turn right at the very bottom of a steep hill, which the cars then have to climb, turning left as they go light over the brow.
Lateral G-forces are in the region of 5G as drivers flick through the direction changes at about 180mph.
The corner is not as big a challenge as it was, as the high levels of aerodynamic downforce of the current cars mean most can take it flat out - at least without DRS deployed.
But Red Bull driver Mark Webber still describes it as an "awesome challenge" in his BBC Sport column, which will be published on Thursday.
The Australian says: "The reason it's so massively rewarding for the drivers is there is a huge plunge down into the bottom of the corner at full speed - we're in top gear approaching 200mph - and then you climb the wall on the other side and pop out of the top.
"Irrespective of how comfortable it is, that's still an amazing sensation, and you need total concentration to make sure the car is positioned correctly - it's three kinks that you need to line up and get right.
"You really don't want to be going off there, even with the increased safety we have these days."
The DRS was not introduced into F1 until this year, but last year many cars were fitted with a device called an F-duct that had a similar effect.
These were operated in many cars by the driver taking his hand off the steering wheel, and the FIA was concerned to discover that many were negotiating Eau Rouge with the F-duct deployed.