Narrative:

I was passenger in a rutan varieze experimental homebuilt aircraft. Fuel was offloaded to reduce takeoff weight; and we were at the maximum authorized gross weight of the aircraft. The aircraft had been fitted approximately one year and 25 flying hours ago with a non-certified digital airspeed indicator (asi). Nothing else was connected to the pitot system. We used most of the 3;300 ft runway for takeoff roll. Asi began to give incorrectly low indications sometime during the late takeoff roll or early climb out. Pilot did not immediately realize the nature of the problem; believing it to be poor performance due to max weight condition. He pitched down in an attempt to maintain airspeed; coming within 50 ft of treetops off departure end of runway. It took some 30 seconds for him to understand the issue and ignore the erroneous asi; after which we climbed to a safe altitude. A 45 minute sightseeing/aircraft demo flight was conducted; during which the asi went through phases of indicating apparently correct and grossly incorrect readings. This type of aircraft requires a rather high landing speed (approximately 90 mph) and is known to be sensitive to excess energy on landing because it is aerodynamically 'clean'. Pilot also reported that it is difficult to land in a crosswind. Due to max gross weight condition; lack of reliable airspeed indicator; short runway and gusting direct crosswind; we elected to divert for landing at a nearby field which has a longer runway almost directly into wind. Approach was made by 'feel' and with reference to GPS ground speed rather than asi; although the asi did appear to be indicating correctly at that point. Landing was uneventful. Inspection of the pitot system on the ground did not reveal any blockages; although we believed the faulty indications to be consistent with a blockage such as an insect in the system. We speculate that there might be a blockage inside the asi instrument. The pilot returned solo without me so as to reduce weight. The asi appeared to indicate correctly on the return flight. My main reason for submitting this report is to highlight the need to cross-check plausibility of instrument readings even during critical; high-workload phases of the flight. We are taught that during climb out under max gross weight conditions; it's very important to maintain vx for best terrain/obstruction clearance. In this case that attempt; based on incorrect airspeed information; led to reduced obstruction separation. Earlier recognition and isolation of the faulty instrument would have improved safety. It's worth noting that visual cues were important in recognizing the nature of the problem (looking outside; 'there's no way we're only doing 60 mph'). Had the takeoff been made under IMC; we would probably have hit the trees.

Related reports:

Google
 

Original NASA ASRS Text

Title: VariEze had an airspeed indicator malfunction during takeoff and climb resulting in the pilot flying pitching over to tree top level to regain airspeed before the fault was detected.

Narrative: I was passenger in a Rutan VariEze experimental homebuilt aircraft. Fuel was offloaded to reduce takeoff weight; and we were at the maximum authorized gross weight of the aircraft. The aircraft had been fitted approximately one year and 25 flying hours ago with a non-certified digital airspeed indicator (ASI). Nothing else was connected to the pitot system. We used most of the 3;300 FT runway for takeoff roll. ASI began to give incorrectly low indications sometime during the late takeoff roll or early climb out. Pilot did not immediately realize the nature of the problem; believing it to be poor performance due to max weight condition. He pitched down in an attempt to maintain airspeed; coming within 50 FT of treetops off departure end of runway. It took some 30 seconds for him to understand the issue and ignore the erroneous ASI; after which we climbed to a safe altitude. A 45 minute sightseeing/aircraft demo flight was conducted; during which the ASI went through phases of indicating apparently correct and grossly incorrect readings. This type of aircraft requires a rather high landing speed (approximately 90 MPH) and is known to be sensitive to excess energy on landing because it is aerodynamically 'clean'. Pilot also reported that it is difficult to land in a crosswind. Due to max gross weight condition; lack of reliable airspeed indicator; short runway and gusting direct crosswind; we elected to divert for landing at a nearby field which has a longer runway almost directly into wind. Approach was made by 'feel' and with reference to GPS ground speed rather than ASI; although the ASI did appear to be indicating correctly at that point. Landing was uneventful. Inspection of the pitot system on the ground did not reveal any blockages; although we believed the faulty indications to be consistent with a blockage such as an insect in the system. We speculate that there might be a blockage inside the ASI instrument. The pilot returned solo without me so as to reduce weight. The ASI appeared to indicate correctly on the return flight. My main reason for submitting this report is to highlight the need to cross-check plausibility of instrument readings even during critical; high-workload phases of the flight. We are taught that during climb out under max gross weight conditions; it's very important to maintain Vx for best terrain/obstruction clearance. In this case that attempt; based on incorrect airspeed information; led to reduced obstruction separation. Earlier recognition and isolation of the faulty instrument would have improved safety. It's worth noting that visual cues were important in recognizing the nature of the problem (looking outside; 'there's no way we're only doing 60 MPH'). Had the takeoff been made under IMC; we would probably have hit the trees.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.