Problem description & analysis:
The column below contains numeric values only:

   A
1 13
2 21
3 46
4 21
5 49
6 9
7 34
8 23
9 6
10 1
11 37
12 49
13 42
14 40
15 15
16 31
17 17
18 1147
19 18
20 30
21 22
22 4
23 25
24 19
25 13
26 27
27 38
28 30
29 16
30 12
31 23
32 3
33 23
34 19
35 14
36 46
37 23
38 37
39 38
40 28

We need to find out the maximum value and the 10 neighboring members both before and after it. Remember to perform out of bounds check as it is possible that the actual number of eligible values is less than 10.

   A
1 23
2 6
3 1
4 37
5 49
6 42
7 40
8 15
9 31
10 17
11 1147
12 18
13 30
14 22
15 4
16 25
17 19
18 13
19 27
20 38
21 30

Solution:
Use SPL XLL to enter the formula below:

=spl("=p=(d=?).pmax(),d.calc(p,~[-10:10])",A1:A40)

As shown in the picture below:

Explanation:
pmax()function gets the position of the maximum value. calc() function performs the computation according to the specified positions; ~ represents the current member, and [] gets members according to the interval specified by the relative positions, which automatically prevents the array index out of bounds.