Air Berlin's share price fell 28% during the first six months of 2012 even as the German carrier's 'Shape & Size' cost-cutting programme exceeded its target.
The stock had lost 5.2% of its value by the end of the first quarter, following the injection of new capital in January when Etihad Airways increased its shareholding from 2.99% to 29.21%.
Air Berlin's share price subsequently fell from €2.37 to €1.80 during the second quarter - amounting to a fall of 28% from its €2.50 value at the end of 2011.
Air Berlin blames the "very disappointing performance" on weak earnings during the first quarter, as well as Germany's aviation tax and the delay in opening Berlin's new airport.
The carrier had planned to increase capacity by 8% in the capital, timing its expansion for the move to Berlin Brandenburg International airport that was due to open on 3 June.
But with Brandenburg's operator postponing the launch to March 2013, Air Berlin has struggled to realise this growth at its existing, much smaller Tegel base. Acknowledging the potential for further delays, the airline says it has made preparations to use Tegel for an indefinite amount of time.
Meanwhile, its 'Shape & Size' fleet reduction and cost-cutting programme has exceeded its €45 million target by €5 million. The target for the whole year has therefore been increased to €230 million.
Air Berlin also wants to "notably" improve equity and liquidity through the sale of aircraft. Shareholder equity at the end of June had fallen 60% year-on-year to €101 million, which the airline blames partly on unfavourable reporting dates. Equity ratio dropped from 11.2% at the end of 2011 to 4% in June.
Nevertheless, chief executive Hartmut Mehdorn predicts that the company will achieve a better equity ratio at the end of this year compared with 2011.