backwards作形容词修饰名词，是从上个世纪60年代开始流行的，目前使用的人越来越多，主要是在英国。我有时在外媒会看到这种用法。当然不如backward更常见。因此，很多词典没有收录这种用法，包括the Free Dictionary. 

经查，柯林斯词典提供了相关解释。https://www.collinsdictionary.com/dictionary/english/backwards 

Backwards is also an adjective.

我再给网友提供几个外刊例句供参考：

Two digital to analogue converters were installed, controlling both forwards/backwards motion and the yaw of the vehicle, respectively. 

This backwards motion is an optical illusion.

Rhoads took a backwards step toward the door.

They mounted the hill, from whose crest Vixen took one last backwards look at the wide wild land that lay behind them.

The freedictionary:

1. 'backwards'

If you move or look backwards, you move or look in the direction your back is facing.

The hummingbird can fly backwards.

He overbalanced and stepped backwards onto a coffee cup.

Lucille looked backwards at the once-lovely site where her great-great-grandparents' graves had lain.

If you do something backwards, you do it the opposite way to the usual way.

Listen to the tape backwards.

2. 'backward'

Speakers of American English sometimes say backward instead of 'backwards'.

The snout hit Hooper in the chest and knocked him backward.

In both British and American English, backward is an adjective. A backward movement or look is one in which someone or something moves or looks backwards.

She took a backward step.

Without a backward glance, he walked away.

When backward is an adjective, it can only be used in front of a noun.

由以上内容可知，backwards是副词，backward为形容词。但美国英语也把backward用为副词。换句话说，作状语或名词后置定语时，用backwards或backward都可以。但如果作名词的前置定语，则无论美式英语还是英式英语都只能用形容词backward。所以，以上二句中都是形容词作定语，backwards应改为backward。