Commuters using the Piccadilly Line are still experiencing severe delays - and they're set to continue for the foreseeable future.
Severe delays while trains are being repaired. Services can be up to 15 mins apart or 20 mins on Uxbridge branch.— Piccadilly line (@piccadillyline) December 2, 2016
TfL later revealed that the train shortage was caused by the fact that around half the Piccadilly Line fleet had been taken out of service for repairs.
The RMT union has called for the line to be closed completely until the repairs are completed, a demand that was shot down by TfL bosses.
So what's gone wrong?
Wet leaves and cold or wet weather causes train tracks to become slippery, and when that happens, the Piccadilly Line train wheels can sometimes lock when braking, damaging both the wheels and the tracks.
TfL says a longer-than-usual leaf-fall period this year has led to more damage than before, and the recent bad weather caused by Storm Angus didn't help either.
And because Piccadilly Line trains are some of the oldest on the Tube network, they don't have the technology that can reduce the impact of braking in cold and wet conditions.
The Piccadilly Line goes through leafy London
According to TfL, "some areas of the Piccadilly line are also particularly surrounded by leaf-shedding trees, particularly on the Rayners Lane branch and between Oakwood/Cockfosters, so the problem is more pronounced here".
There's a backlog
"We’re working around the clock to fix the trains so that we can return to a good service as quickly as possible," Piccadilly Line boss Tony Matthews said last week.
Around two trains are being put back into service per day, TfL has said. However, there is currently a backlog of wheel repairs because of high levels of faults.
When will it be back to normal?
"We've recently had two colder evenings which means that most leaves have now fallen," TfL said.
"This should mean that fewer trains will become damaged. We will be able to return more trains to the line each day - however, there is a backlog of trains. We are working to restore a full, timetabled service as quickly as possible."
So basically... nobody knows.