In recent years CAA has authorised the use of Warfarin by Air Crew and Air traffic Controllers. This has paved the way for the acceptance of conditions that would otherwise carry an excessive risk of incapacitation without antithrombotic prophylaxis.

The use of Warfarin however does carry risks. Too low an INR and the risk posed by the condition being treated becomes excessive. Too high an INR and the risk inherent to Warfarin becomes excessive. This is illustrated in the following graph in the case of AF.

Use of Warfarin graph

Thus it is critical, when certifying anyone on Warfarin, to ensure perfect compliance with:

  • Dosage, and
  • INR testing, and
  • Any condition or restriction imposed on the Medical Certificate.

Information to be provided

  • INR results, dates of determination and doses for the past 6 months; at least the last 6 results should be provided;
  • Confirmation of absence of any complication relating to the use of Warfarin or the condition being treated;
  • All information relating to the condition being treated, in accordance with any relevant guidelines outlined in other parts of this manual.


An applicant taking Warfarin should be considered as having a condition that is of aeromedical significance, unless:

  • The condition being treated is not of aeromedical significance while being treated;
  • There has been no episode of spontaneous or major bleeding;
  • A condition of surveillance is imposed, requiring regular INR determinations, at least once a month and within 10 days prior to flying, and a diary kept;
  • Four out of the last five INR determination results are within the therapeutic range for the condition being treated (i.e.: 2.0 - 3.0 or 2.5 - 3.5 as appropriate);
  • A restriction is imposed preventing the exercises of the licence holder’s privileges four out of the last five INR results are within the appropriate therapeutic range;
  • A restriction 'not valid for single pilot air operations carrying passengers' is imposed in the case of a Class 1 medical certificate.