Table:
0
A
B
C
D
E
1
AIRLINE
AIRLINE (in Arabic)
ICAO
CALLSIGN
COMMENCED OPERATIONS
2
Karthago Airlines
قرطاج للطيران
KAJ
KARTHAGO
2001
3
Nouvelair
الطيران الجديد تونس
LBT
NOUVELAIR
1989
4
TunisAir Express
الخطوط التونسية السريعة
TUX
TUNEXPRESS
1991
5
Syphax Airlines
سيفاكس أيرلاينز
SYA
SYPHAXAIR
2011
6
Tunisair
الخطوط التونسية
TAR
TUNAIR
1948
7
Tunisavia
الشركة التونسية للنقل و الخدمات الجوية
TAJ
TUNISAVIA
2010

Questions and formulas:
Question: What is the ICAO with commenced operations before 1989?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1<1989),3))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E7,E2:E7<1989),3))
Level: medium
Question: What is the lowest commenced operations that has a nouvelair callsign?
Formula: MINIFS(E1,D1,"nouvelair")
Formula2: MINIFS(E2:E7,D2:D7,"nouvelair")
Level: easy
Question: What callsign has commenced operations in 2011?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1=2011),4))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E7,E2:E7=2011),4))
Level: medium