+Sputnik 57 Posted December 12, 2005 Share Posted December 12, 2005 I've been using a 60C for over a year, and have found that the ETA to a point that I am driving to is reasonably accurate if there is no traffic. From what I understand, the unit uses road speed, not actual speed, to compute your ETA. Last week I flew to Dallas and San Antonio, and was using my GPSr on Southwest Airline flights. Since we were in heavy clouds, I couldn't pursue my usual pasttime of identifying ground features from the map, and out of boredom, I started watching the Time to Destination reading, comparing to my our actual speed. I took a few readings on the Dallas flight, and then, flying home from San Antonio, I took more readings. The flight is pretty short from the time of the "OK to use PEDs" announcement to the "discontinue and store all PEDs" announcement. Based upon my distance to Hobby airport and the unit's estimated travel time, I computed the assumed speed and compared it to my actual speedHere are my findings: ===================================================== Time to Waypoint 25 20 18 15 12 10 9 6 5 Distance to Wpt 164 138 128 118 87.9 63.6 53.4 31.2 27.0 Actual Speed 460 510 523 541 501 436 399 346 340 Assumed Speed 394 414 427 472 440 382 356 312 324 (I know the table is hard to read since the forum strips extra spaces--sorry about that). From the data, you would think that an average speed is being used. For example, from 18 to 15 minutes out, the actual ground speed went from 523 to 541 (we must have had a tail wind--I rarely see speeds much over 505 or so). The "assumed speed" changed from 427 to 472. When the actual goes to 501 at 12 minutes out, the "assumed speed" reduces to 440. But look at the last two entries. Speed declines from 346 to 340, but the "assumed speed" goes from 312 to 324. Any ideas? Or should I just stick to the in-flight magazine and forget about this? Quote Link to comment
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.