The WRU chairman is leading a team of 16 to the top of the Tanzanian peak to help raise £100,000 for the NSPCC's Full Stop campaign.
But after two days of climbing the 46-year-old Pickering admitted that he and his colleagues were "absolutely knackered".
Speaking from their campsite nearly half-way up Kilimanjaro on Friday, Pickering hinted for the first time that he feared not everyone in the team would make it to the summit.
"Everyone was in a pretty jovial mood when we left, but as we flew into Tanzania the size of the task ahead of us hit firmly between the eyes," explained Pickering.
"We were cruising at 17,000 ft and yet we still had to look up to the snow covered peak of Kilimanjaro - it was an awesome sight. That instantly turned what many of us thought was going to be a bit of a jaunt into a far more serious exercise.
"There is an easy way to climb Kilimanjaro, but our leader, Lt Col Dicke Davis, chose the army route for us and that meant we spent the first day clambouring virtually on our hands and knees through the rain forest.
"We did nine solid hours to reach our camp. At the end of it we just put up our tents, went straight to bed and didn't even contemplate eating.
"I don't think I have ever been so exhausted in my life. Even JPR Williams found it tough going!
"It took us two days to reach 2,180 metres and the worry is that with fresh snowfall at the peak in recent days the climb is only going to get harder and colder.
"But we haven't come all this way, or put in so much training, to be beaten by this moutnain. We are all determined to push ourselves to the limits to raise the final £30,000 we need to break through the six-figure fund-raising barrier."
Pickering and co were told by Lt Col Davis just before they left last Monday that they faced a diffiuclt task because their route had to be changed following a series of recent deaths on their origianl path.
"Three people had been killed recently taking our initial route up the mountain so we were forced to factor that into our planning. There was a problem with some rock falls and we decided to alter our plans accordingly," said Lt Col Davis.
"We are still aiming to reach the summit (19,335 ft or 5,895 metres)in five days. It is turning out to be exactly what I promised them all - the most physically demanding activity that 99% of them have ever undertaken in their lives.
"To be honest, I'm not sure that everyone is going to make it to the top, although that our collective goal. We started as a group and we want to end as a group.
"As well as being physically challenging, there are also moments of potential high risk and danger. This is no easy ride and as we climb higher so the risk of altitude sickness will come into play."
While temperatures are high at the bottom of the mountain, by the time the climbers reach the summit the evening temperatures can plummit well below zero.
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