What is an appropriate IFR altitude for an aircraft on a true heading of 178 degrees?

When determining an appropriate IFR (Instrument Flight Rules) altitude for an aircraft, the true heading plays an essential role in ensuring safe vertical separation between aircraft. In the U.S. and many places around the world under IFR, altitudes are assigned based on the magnetic heading due to the use of magnetic compass systems in aircraft.

For IFR operations, the "odd" altitude rule applies for aircraft flying on a magnetic heading of 180 degrees or above (but less than 360 degrees). This translates to needing to fly at an even altitude within the airspace.

With a true heading of 178 degrees, the magnetic heading must be assessed to determine the correct altitude. If the magnetic declination (the angle difference between true north and magnetic north) is not provided or cannot be determined, assessing the appropriate altitude becomes impossible. This is because you cannot ascertain whether the aircraft needs to use an odd or even altitude without knowing the magnetic heading, which is necessary for compliance with air traffic regulations and separation standards.

Thus, it's correct to state that without knowing the magnetic heading, a definitive IFR altitude cannot be assigned. The answer indicates the importance of magnetic alignment in altitude assignments and emphasizes the need for complete information when dealing with IFR protocols.