The impact of Easter on yields at European airlines is likely to be negative, according to analysts at UBS.Yields are typically calculated by dividing passenger revenue by revenue passenger miles. "North Atlantic yield development shows negative growth in April while February, March and May is expected to come in positive," said UBS analysts Jarrod Castle and Anuj Mehrotra. "We think the timing of Easter has had an impact on April data given the impact Easter has on premium travel (less premium travel over Easter period)," they said.Despite this, UBS believes that "capacity discipline" is holding with positive trends highlighted, while tailwinds from falling jet fuel prices should continue to benefit airlines in 2014.The bank said it remains positive on UK-listed airline peers IAG and easyJet. These stocks were down 1% and 0.6% by 10:20 on Monday morning, respectively.BC