“…Recently, Bonnabel, Martin, and Rouchon (2006), Vik and Fossen (2001), Zhao and Slotine (2005), Benallegue et al (2008), Besnard et al (2007), Boutayeb et al (2008), Benzemrane et al (2007), Benzemrane (2009), Madani and Benallegue (2007) and Pflimlin et al (2007) have proposed observers to be implemented on UAVs. The critical issue in this domain comes from the fact that the translation velocity is classically known as non-observable.…”