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We present a pilot HI survey of 17 Planck Galactic Cold Clumps (PGCCs) with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). HI Narrow Self-Absorption (HINSA) is an effective method to detect cold HI being mixed with molecular hydrogen H$_2$ and improves our understanding of the atomic to molecular transition in the interstellar medium. HINSA was found in 58\% PGCCs that we observed. The column density of HINSA was found to have an intermediate correlation with that of $^{13}$CO, following $\rm log( N(HINSA)) = (0.52\pm 0.26) log(N_{^{13}CO}) + (10 \pm 4.1) $. HI abundance relative to total hydrogen [HI]/[H] has an average value of $4.4\times 10^{-3}$, which is about 2.8 times of the average value of previous HINSA surveys toward molecular clouds. For clouds with total column density N$\rm_H >5 \times 10^{20}$ cm$^{-2}$, an inverse correlation between HINSA abundance and total hydrogen column density is found, confirming the depletion of cold HI gas during molecular gas formation in more massive clouds. Nonthermal line width of $^{13}$CO is about 0-0.5 km s$^{-1}$ larger than that of HINSA. One possible explanation of narrower nonthermal width of HINSA is that HINSA region is smaller than that of $^{13}$CO. Based on an analytic model of H$_2$ formation and H$_2$ dissociation by cosmic ray, we found the cloud ages to be within 10$^{6.7}$-10$^{7.0}$ yr for five sources., 11 pages, 11 figures, accepted by the Research in Astronomy and Astrophysics (RAA)

On-The-Fly (OTF) observing is one of the five kinds of operation mode owned by Five-hundred-meter Aperture Spherical Radio Telescope (FAST). In order to guarantee the active feed receiver move stably during the OTF observation, its trajectory planning was dealt with in this paper. Considering the trajectory in local coordinate system is complex, the paper planned its trajectory planning in the equatorial coordinate system. For the Earth's rotation, in order to guarantee the active feed receiver to start smoothly from a standstill and to soft-stop stably in the specified time when scanning along the declination, the right ascension and declination were planned with the double S velocity profile at the same time. The resulting trajectory is ensured the continuation in position, velocity and acceleration under local coordinate system, meanwhile, considering the execute ability of the mechanism, the trajectory respect specified limits in velocity, acceleration and jerk. An example and the comparison between the original trajectory and the planned trajectory are given to illustrate the advantage of the presented approach.